Membranes of polyurethane based materials including polyester polyols

ABSTRACT

The present invention relates to membranes including an urethane including a polyester polyol, wherein the membrane has a gas transmission rate of 15.0 or less for nitrogen gas wherein the membrane has an average thickness of approximately 20.0 mils. Under certain embodiments, the membranes include blends of one or more polyester polyol based thermoplastic urethanes and one or more barrier materials. The membranes can be employed in a variety of applications and can be used as either monolayers or multi-layered laminates.

FIELD OF THE INVENTION

[0001] The present application is a continuation-in-part of U.S. patentapplication Ser. No. 08/475,275 entitled “Membranes Including A BarrierLayer Employing Polyester Polyols,” filed on Jun. 7, 1995, which ishereby expressly incorporated herein by reference.

[0002] The present invention relates to membranes and, moreparticularly, to membranes which, under certain embodiments, serve toselectively control the diffusion of gases through the membrane.Additionally, the membrane not only selectively controls the diffusionof gases through the membrane, but also allows for the controlleddiffusion of gases normally contained in the atmosphere.

BACKGROUND OF THE INVENTION

[0003] Membranes, and more particularly, membranes useful for containingfluids, including liquids and/or gases, in a controlled manner, havebeen employed for years in a wide variety of products ranging frombladders useful in inflatable objects, including vehicle tires andsporting goods for example; to accumulators used on heavy machinery; tocushioning devices useful in footwear. Regardless of the intended use,membranes must generally be flexible, resistant to environmentaldegradation and exhibit excellent gas transmission controls. Often,however, materials which exhibit acceptable flexibility characteristicstend to have an unacceptably low level of resistance to gas permeation.In contrast, materials which exhibit an acceptable level of resistanceto gas permeation tend to have an unacceptably low level of flexibility.

[0004] In an attempt to address the concerns of both flexibility andimperviousness to gases, U.S. Pat. No. 5,036,110 which issued Jun. 30,1991, to Moreaux describes resilient membranes for fittinghydropneumatic accumulators. According to Moreaux '110, the membranedisclosed consists of a film formed from a graft polymer which is thereaction product of an aromatic thermoplastic polyurethane with acopolymer of ethylene and vinyl alcohol, with this film being sandwichedbetween layers of thermoplastic polyurethane to form a laminate. WhileMoreaux '110 attempts to address the concerns in the art relating toflexibility and imperviousness to gases, a perceived drawback of Moreauxis that the film described is not processable utilizing conventionaltechniques such as sheet extrusion, for example. Thus, the presentinvention is directed to membranes which are flexible, have goodresistance to gas transmission, and under certain embodiments areprocessable into laminates utilizing conventional techniques such assheet extrusion which are highly resistant to delamination.

[0005] While it should be understood by those skilled in the art uponreview of the following specification and claims that the membranes ofthe present invention have a broad range of applications, including butnot limited to bladders for inflatable objects such as footballs,basketballs, soccer balls, inner tubes; substantially rigid flotationdevices such as boat hulls; flexible floatation devices such as tubes orrafts; as a component of medical equipment such as catheter balloons;fuel lines and fuel storage tanks; various cushioning devices such asthose incorporated as part of an article of footwear or clothing; aspart of an article of furniture such as chairs and seats, as part of abicycle or saddle, as part of protective equipment including shin guardsand helmets; as a supporting element for articles of furniture and, moreparticularly, lumbar supports; as part of a prosthetic or orthopedicdevice; as a portion of a vehicle tire and particularly, the outer layerof the tire, as well as being incorporated as part of certain recreationequipment such as components of wheels for in-line or roller skates, toname a few, still other applications are possible. For example, onehighly desirable application for the membranes of the present inventioninclude their use in forming accumulators which are operable under highpressure environments such as hydraulic accumulators as will bediscussed in greater detail below.

[0006] For convenience, but without limitation, the membranes of thepresent invention will hereinafter generally be described in terms ofeither accumulators or in terms of still another highly desirableapplication, namely for cushioning devices used in footwear. In order tofully discuss the applicability of the membranes in terms of cushioningdevices for footwear, a description of footwear in general is believedto be necessary.

[0007] Footwear, or more precisely, shoes generally include two majorcategories of components namely, a shoe upper and the sole. The generalpurpose of the shoe upper is to snugly and comfortably enclose the foot.Ideally, the shoe upper should be made from an attractive, highlydurable, yet comfortable material or combination of materials. The sole,which also can be made from one or more durable materials, isparticularly designed to provide traction and protect the wearer's feetand body during use. The considerable forces generated during athleticactivities require that the sole of an athletic shoe provide enhancedprotection and shock absorption for the feet, ankles and legs of thewearer. For example, impacts which occur during running activities cangenerate forces of up to 2-3 times the body weight of an individualwhile certain other activities such as, for example, playing basketballhave been known to generate forces of up to approximately 6-10 times anindividual's body weight. Accordingly, many shoes and, moreparticularly, many athletic shoes are now provided with some type ofresilient, shock-absorbent material or shock-absorbent components tocushion the user during strenuous athletic activity. Such resilient,shock-absorbent materials or components have now commonly come to bereferred to in the shoe manufacturing industry as the midsole.

[0008] It has therefore been a focus of the industry to seek midsoledesigns which achieve an effective impact response in which bothadequate shock absorption and resiliency are appropriately taken intoaccount. Such resilient, shock-absorbent materials or components couldalso be applied to the insole portion of the shoe, which is generallydefined as the portion of the shoe upper directly underlining theplantar surface of the foot.

[0009] A particular focus in the footwear manufacturing industry hasbeen to seek midsole or insert structure designs which are adapted tocontain fluids, in either the liquid or gaseous state, or both. Examplesof gas-filled structures which are utilized within the soles of shoesare shown in U.S. Pat. Nos. 900,867 entitled “Cushion for Footwear”which issued Oct. 13, 1908, to Miller; 1,069,001 entitled “CushionedSole and Heel for Shoes” which issued Jul. 29, 1913, to Guy; 1,304,915entitled “Pneumatic Insole” which issued May 27, 1919, to Spinney;1,514,468 entitled “Arch Cushion” which issued Nov. 4, 1924, to Schopf;2,080,469 entitled “Pneumatic Foot Support” which issued May 18, 1937,to Gilbert; 2,645,865 entitled “Cushioning Insole for Shoes” whichissued Jul. 21, 1953, to Towne; 2,677,906 entitled “Cushioned Inner Solefor Shoes and Method of Making the Same” which issued May 11, 1954, toReed; 4,183,156 entitled “Insole Construction for Articles of Footwear”which issued Jan. 15, 1980, to Rudy; 4,219,945 entitled “Footwear” whichissued Sep. 2, 1980, also to Rudy; 4,722,131 entitled “Air Cushion ShoeSole” which issued Feb. 2, 1988, to Huang; and 4,864,738 entitled “SoleConstruction for Footwear” which issued Sep. 12, 1989, to Horovitz. Aswill be recognized by those skilled in the art, such gas filledstructures often referred to in the shoe manufacturing industry as“bladders” typically fall into two broad categories, namely (1)“permanently” inflated systems such as those disclosed in U.S. Pat. Nos.4,183,156 and 4,219,945 and (2) pump and valve adjustable systems asexemplified by U.S. Pat. No. 4,722,131. By way of further example,athletic shoes of the type disclosed in U.S. Pat. No. 4,182,156 whichinclude “permanently” inflated bladders have been successfully soldunder the trade mark “Air-Sole” and other trademarks by Nike, Inc. ofBeaverton, Oreg. To date, millions of pairs of athletic shoes of thistype have been sold in the United States and throughout the world.

[0010] The permanently inflated bladders have historically beenconstructed under methods using a flexible thermoplastic material whichis inflated with a large molecule, low solubility coefficient gasotherwise referred to in the industry as a “super gas.” By way ofexample, U.S. Pat. No. 4,340,626 entitled “Diffusion Pumping ApparatusSelf-Inflating Device” which issued Jul. 20, 1982, to Rudy, which isexpressly incorporated herein by reference, discloses selectivelypermeable sheets of film which are formed into a bladder and thereafterinflated with a gas or mixture of gases to a prescribed pressure whichpreferably is above atmospheric pressure. The gas or gases utilizedideally have a relatively low diffusion rate through the selectivelypermeable bladder to the exterior environment while gases such asnitrogen, oxygen and argon which are contained in the atmosphere andhave a relatively high diffusion rate are able to penetrate the bladder.This produces an increase in the total pressure within the bladder, bythe addition of the partial pressures of the nitrogen, oxygen and argonfrom the atmosphere to the partial pressures of the gas or gasescontained initially injected into the bladder upon inflation. Thisconcept of a relative one-way addition of gases to enhance the totalpressure of the bladder is now known as “diffusion pumping.”

[0011] With regard to the systems utilized within the footwearmanufacturing industry prior to and shortly after the introduction ofthe Air-Sole™ athletic shoes, many of the midsole bladders consisted ofa single layer gas barrier type films made from polyvinylidene chloridebased materials such as Saran® (which is a registered trademark of theDow Chemical Co.) and which by their nature are rigid plastics, havingrelatively poor flex fatigue, heat sealability and elasticity.

[0012] Still further, bladder films made under techniques such aslaminations and coatings which involve one or more barrier materials incombination with a flexible bladder material (such as variousthermoplastics) can potentially present a wide variety of problems tosolve. Such difficulties with composite constructions include layerseparation, peeling, gas diffusion or capillary action at weldinterfaces, low elongation which leads to wrinkling of the inflatedproduct, cloudy appearing finished bladders, reduced puncture resistanceand tear strength, resistance to formation via blow-molding and/orheat-sealing and RF welding, high cost processing, and difficulty withfoam encapsulation and adhesive bonding, among others.

[0013] Yet another issue with previously known multi-layer bladders isthe use of tie-layers or adhesives in preparing laminates. The use ofsuch tie layers or adhesives generally prevent regrinding and recyclingof any waste materials created during product formation back into anusable product, and thus, also contribute to high cost of manufacturingand relative waste. These and other perceived short comings of the priorart are described in more extensive detail in U.S. Pat. Nos. 4,340,626;4,936,029 and 5,042,176, all of which are hereby expressly incorporatedby reference.

[0014] Previously known multi-layer bladders which specificallyeliminate adhesive tie layers have been known to separate or de-laminateespecially along seams and edges. Thus, it has been a relatively recentfocus of the industry to develop laminated bladders which reduce oreliminate the occurrence of delamination ideally without the use of a“tie layer.” In this regard, the cushioning devices disclosed inco-pending U.S. application patent Ser. Nos. 08/299,286 and 08/299,287eliminate adhesive tie layers by providing membranes including a firstlayer of thermoplastic urethane and a second layer including a barriermaterial such as a copolymer of ethylene and vinyl alcohol whereinhydrogen bonding occurs over a segment of the membranes between thefirst and second layers. While the membranes disclosed in U.S. patentapplication Ser. No. 08/299,287 and the laminated flexible membranes ofU.S. patent application Ser. No. 08/299,286 are believed to offer asignificant improvement in the art, still further improvements areoffered according to the teachings of the present invention.

[0015] With the extensive commercial success of the products such as theAir-Sole™ shoes, consumers have been able to enjoy products with a longservice life, superior shock absorbency and resiliency, reasonable cost,and inflation stability, without having to resort to pumps and valves.Thus, in light of the significant commercial acceptance and success thathas been achieved through the use of long life inflated gas filledbladders, it is highly desirable to develop advancements relating tosuch products. One goal then is to provide flexible, “permanently”inflated, gas-filled shoe cushioning components which meet, andhopefully exceed, performance achieved by such products as the Air-Sole™athletic shoes offered by Nike, Inc.

[0016] An accepted method of measuring the relative permeance,permeability and diffusion of different film materials is set forth inthe procedure designated as ASTM D-1434-82-V. According to ASTMD-1434-82-V, permeance, permeability and diffusion are measured by thefollowing formulas: $\begin{matrix}{\frac{\left( {{quantity}\quad {of}\quad {gas}} \right)}{({area}) \times ({time}) \times \left( {{press}.\quad {diff}.} \right)} = {\begin{matrix}{Permeance} \\{({GTR})/\left( {{press}.\quad {diff}.} \right)}\end{matrix} = \frac{{cc}.}{\left( {{sq}.\quad m} \right)\left( {24\quad {hr}} \right)({Pa})}}} & \text{Permeance} \\{\frac{\left( {{quantity}\quad {of}\quad {gas}} \right) \times \left( {{film}\quad {thick}} \right)}{({area}) \times ({time}) \times \left( {{press}.\quad {diff}.} \right)} = {\begin{matrix}{Permeability} \\{({GTR}) \times {\left( {{film}\quad {thick}} \right)/\left( {{press}.\quad {diff}.} \right)}}\end{matrix} = \frac{({cc})({mil})}{\left( {{sq}.\quad m} \right)\left( {24\quad {hr}} \right)({Pa})}}} & \text{Permeability} \\{\frac{\left( {{quantity}\quad {of}\quad {gas}} \right)}{({area}) \times ({time})} = {\begin{matrix}{{Gas}\quad {Transmission}\quad {Rate}} \\({GTR})\end{matrix} = \frac{cc}{\left( {{sq}.\quad m} \right)\left( {24\quad {hr}} \right)}}} & \text{Diffusion}\end{matrix}$

[0017] By utilizing the above listed formulas, the gas transmission ratein combination with a constant pressure differential and the film'sthickness, can be utilized to define the movement of gas under specificconditions. In this regard, the preferred gas transmission rate (GTR)for a membrane having an average thickness of approximately 20.0 milssuch as those useful for forming a cushioning device used as a shoecomponent which seeks to meet the rigorous demands of fatigue resistanceimposed by heavy and repeated impacts will preferably have a gastransmission rate (GTR) of 15.0 or less for nitrogen gas according toASTM D-1434-82-V. More preferably, the membranes will have a GTR of lessthan about 2.0 at an average thickness of 20 mils.

[0018] It is, therefore, one object of the present invention to providemembranes including both single layer and multi-layer constructionswhich offer enhanced flexibility, durability and resistance to theundesired transmission of fluids therethrough.

[0019] It is another object of the present invention to providemembranes which can be inflated with a gas such as nitrogen wherein themembrane provides for a gas transmission rate value of 15.0 or less,based on a 20 mils average thickness.

[0020] It is still another object of the present invention to providemembranes, particularly those employed as cushioning devices, having arelatively high degree of transparency.

[0021] It is another object of the present invention to providemonolayer membranes which are readily processable into various products.

[0022] It is yet another object of the present invention to providemonolayer membranes and, under certain applications, multi-layermembranes which are re-processable and repairable.

[0023] It is yet another object of the present invention to providemembranes which can be formed into laminated objects such as cushioningdevices or accumulators, among others, which better resist delaminationand also may not require a tie layer between the layers.

[0024] It is a further object of the present invention to providemembranes which are formable utilizing various techniques including, butnot limited to, blow-molding, tubing, sheet extrusion, vacuum-forming,heat-sealing, casting, liquid casting, low pressure casting, spincasting, reaction injection molding and RF welding.

[0025] Still another object of the present invention is to providemembranes which prevent gas from escaping along interfaces between thelayers in laminated embodiments and particularly along seems viacapillary action.

[0026] It is yet another object of the present invention to provide amembrane which allows for footwear processing such as encapsulation of amembrane within a formable material.

[0027] While the aforementioned objects provide guidance as to possibleapplications and advantages for the membranes of the present invention,it should be recognized by those skilled in the art that the recitedobjects are not intended to be exhaustive or limiting.

SUMMARY OF THE INVENTION

[0028] To achieve the foregoing objects, the present invention providesmembranes which preferably have one or more of the following: (1) adesirable level of flexibility (or rigidity); (2) a desirable level ofresistance to degradation caused by moisture; (3) an acceptable level ofimperviousness to fluids which can be in the form of gases, liquids orboth depending mainly on the intended use of the product; and (4)resistance to delamination when employed in a multi-layer structure.Regardless of the membrane embodiment, each membrane in accordance withthe teachings of the present invention includes a layer comprised of apolyester polyol based polyurethane. The aforementioned layer may alsoinclude at least one barrier material selected from the group consistingof co-polymers of ethylene and vinyl alcohol, polyvinylidene chloride,co-polymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, aliphatic and aromatic polyamides, crystalline polymersand polyurethane engineering thermoplastics blended with thepolyurethane prior to forming the membranes.

[0029] The polyester polyol based urethanes employed, if notcommercially available, are preferably formed as the reaction product of(a) one or more carboxylic acids having six or less carbon atoms withone or more diols having six or less carbon atoms; (b) at least oneisocyanate and/or diisocyanate; and (c) optionally, but preferably, oneor more extenders. The polyester polyol may also include a relativelysmall amount of one or more polyfunctional materials such as triolswhich are included as part of the reaction product. In addition to theforegoing, the polyester polyol based urethanes may optionally employone or more of the following: (d) hydrolytic stabilizers; (e)plasticizers; (f) fillers; (g) flame retardants; and (h) processingaids. The resulting polyester polyols formed as a result of the reactionproduct of the one or more carboxylic acids with one or more diolspreferably have repeating units containing eight carbon atoms or less.

[0030] The term “carboxylic acid” as used herein, and unless otherwiseindicated, preferably means a carboxylic acid, and more preferably adicarboxylic acid, having no more than six carbon atoms when reactedwith a diol, wherein the repeating units of the polyester polyol formedby the aforesaid reaction has no more than eight carbon atoms.

[0031] The term “diol” as used herein, and unless otherwise indicated,to preferably mean diols having no more than six carbon atoms whenreacted with a carboxylic acid, wherein the repeating units of thepolyester polyol formed by the aforesaid reaction has no more than eightcarbon atoms.

[0032] The term “polyester polyol” as used herein is intended topreferably mean polymeric polyester polyols having a molecular weight(determined by the ASTM D-4274 method) falling in the range of about 300to about 4,000; more preferably from about 400 to about 2,000; and stillmore preferably between about 500 to about 1,500.

[0033] The term “thermoplastic” as used herein is generally intended tomean that the material is capable of being softened by heating andhardened by cooling through a characteristic temperature range, and assuch in the softened state can be shaped into various articles undervarious techniques.

[0034] The term “thermoset” as used herein is generally intended to meana polymeric material that will not flow upon the application of heat andpressure after it is substantially reacted.

[0035] The term “extender” or “difunctional extender” is used preferablyin the commonly accepted sense to one skilled in the art and includesglycols, diamines, amino alcohols and the like. Preferably, any suchextender or difunctional extender employed in accordance with theteachings of the present invention will have a molecular weightgenerally falling in the range of from about 60 to about 400.

[0036] The term “soft segment” as used herein is generally intended tomean the component of the formulation exhibiting a molecular weight fromapproximately 300-4000 that contains approximately two or more activehydrogen groups per molecule prior to reaction that provides theelastomeric character of the resulting polymers.

[0037] Preferably, the membranes described herein may be useful ascomponents for footwear. In such applications, the membranes preferablyare capable of containing a captive gas for a relatively long period oftime. In a highly preferred embodiment, for example, the membrane shouldnot lose more than about 20% of the initial inflated gas pressure over aperiod of approximately two years. In other words, products inflatedinitially to a steady state pressure of between 20.0 to 22.0 psi shouldretain pressure in the range of about 16.0 to 18.0 psi for at leastabout two years.

[0038] Additionally, the materials utilized for products such ascomponents of athletic shoes should be flexible, relatively soft andcompliant and should be highly resistant to fatigue and be capable ofbeing welded to form effective seals typically achieved by RF welding orheat sealing. The material should also have the ability to withstandhigh cycle loads without failure, especially when the material utilizedhas a thickness of between about 5 mils to about 200 mils.

[0039] Another preferred characteristic of the membrane is the abilityto be processable into various shapes by techniques used in high volumeproduction. Among these techniques known in the art are extrusion, blowmolding, injection molding, vacuum molding, rotary molding, transfermolding, pressure forming, heat-sealing, casting, low pressure casting,spin casting, reaction injection molding and RF welding, among others.

[0040] As discussed above, a preferred characteristic of the membranes,whether monolayer or multi-layer in construction, is their ability underembodiments to be formed into products which are inflated (such ascushioning devices for footwear) and which control diffusion of mobilegases through the membrane. By the present invention, not only are supergases usable as captive gases, but nitrogen gas and air, among others,may also be used as captive gases due to the performance of thematerials.

[0041] Another feature of the monolayer membranes of the presentinvention is elimination of many of the processing concerns presented bymulti-layer embodiments. Monolayer membranes can generally be processedwithout requiring special mechanical adapters for processing equipmentand other process controls. Further, products formed from monolayerembodiments are not subject to delamination and can, at least in thecase of thermoplastics, be recycled and reground for subsequentinclusion in a variety of products.

[0042] With regard to multiple layer embodiments, a further feature ofthe present invention is the enhanced bonding which can occur betweencontiguous layers, thus, potentially eliminating the need for adhesivetie layers. This so-called enhanced bonding is generally accomplished bybringing the first and second layers together into intimate contactusing conventional techniques wherein the materials of both layers haveavailable functional groups with hydrogen atoms that can participate inhydrogen bonding such as hydrogen atoms in hydroxyl groups or hydrogenatoms attached to nitrogen atoms in urethane groups and various receptorgroups such as oxygen atoms in hydroxyl groups, carboxyl oxygens inurethane groups and ester groups, and chlorine atoms in PVDC, forexample. Such laminated membranes are characterized in that hydrogenbonding is believed to occur between the first and second layers. Forexample, the above described hydrogen bonding will theoretically occurwhere the first layer comprises a polyester polyol based urethane andthe second layer includes a barrier material such as one selected fromthe group consisting of co-polymers of ethylene and vinyl alcohol,polyvinylidene chloride, co-polymers of acrylonitrile and methylacrylate, polyethylene terephthalate, aliphatic and aromatic polyamides,crystalline polymers and polyurethane engineering thermoplastics. Inaddition to the occurrence of hydrogen bonding, it is theorized thatthere will also generally be a certain amount of covalent bondingbetween the first and second layers if, for example, there arepolyurethanes in adjacent layers or if one of the layers includespolyurethane and the adjacent layer includes a barrier material such ascopolymers of ethylene and vinyl alcohol.

[0043] This invention has many other advantages which will be moreapparent from consideration of the various forms and embodiments of thepresent invention. Again, while the embodiments shown in theaccompanying drawings which form a part of the present specification areillustrative of embodiments employing the membranes of the presentinvention, it should be clear that the membranes have extensiveapplication possibilities. Various exemplary embodiments will now bedescribed in greater detail for the purpose of illustrating the generalprinciples of the invention, without considering the following detaileddescription in the limiting sense.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044]FIG. 1 is a side elevational view of an athletic shoe with aportion of the midsole cut away to illustrate a cross-sectional view;

[0045]FIG. 2 is a bottom elevational view of the athletic shoe of FIG. 1with a portion cut away to expose another cross-sectional view;

[0046]FIG. 3 is a section view taken alone line 3-3 of FIG. 1;

[0047]FIG. 4 is a fragmentary side perspective view of one embodiment ofa tubular-shaped, two-layer cushioning device;

[0048]FIG. 5 is a sectional view taken along line 4-4 of FIG. 4;

[0049]FIG. 6 is a fragmentary side perspective view of a secondembodiment of a tubular-shaped, three-layer cushioning device;

[0050]FIG. 7 is a sectional side view taken along line 6-6 of FIG. 6;

[0051]FIG. 8 is a perspective view of a membrane embodiment according tothe present invention formed into a shoe cushioning device;

[0052]FIG. 9 is a side view of the membrane illustrated in FIG. 8;

[0053]FIG. 10 is a perspective view of a membrane embodiment accordingto the present invention formed into a shoe cushioning device;

[0054]FIG. 11 is a side elevational view of a membrane embodimentaccording to the present invention formed into a cushioning device whichis incorporated into a shoe;

[0055]FIG. 12 is a perspective view of the membrane illustrated in FIG.11;

[0056]FIG. 13 is a top elevation view of the membrane illustrated inFIGS. 11 and 12;

[0057]FIG. 14 is a side elevation view of a membrane embodimentaccording to the present invention formed into a cushioning deviceincorporated into a shoe;

[0058]FIG. 15 is a perspective view of the membrane illustrated in FIG.14;

[0059]FIG. 16 is a top view of the membrane illustrated in FIGS. 14 and15;

[0060]FIG. 17 is a perspective view of a membrane embodiment accordingto the teachings of the present invention formed into a shoe cushioningdevice;

[0061]FIG. 18 is a side view of the membrane illustrated in FIG. 17;

[0062]FIG. 19 is a sectional view of a product formed from a laminatedmembrane according to the teachings of the present invention;

[0063]FIG. 20 is a sectional view of a second product manufactured usinga laminated membrane according to the teachings of the presentinvention;

[0064]FIG. 21 is a side elevation view of a sheet co-extrusion assembly;

[0065]FIG. 22 is a cross-sectional view of the manifold portion of thesheet co-extrusion assembly of FIG. 22;

[0066]FIG. 23 is a side elevation view of a tubing co-extrusionassembly;

[0067]FIG. 24 is a sectional view of a monolayer tubular membrane; and

[0068]FIG. 25 is a sectional view of a product formed from a monolayermembrane according to the teachings of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Referring to FIGS. 1-3, there is shown an athletic shoe,including a sole structure and a cushioning device as one example of aproduct formed from a membrane in accordance with the teachings of thepresent invention. The shoe 10 includes a shoe upper 12 to which thesole 14 is attached. The shoe upper 12 can be formed from a variety ofconventional materials including, but not limited to, leathers, vinyls,nylons and other generally woven fibrous materials. Typically, the shoeupper 12 includes reinforcements located around the toe 16, the lacingeyelets 18, the top of the shoe 20 and along the heel area 22. As withmost athletic shoes, the sole 14 extends generally the entire length ofthe shoe 10 from the toe region 20 through the arch region 24 and backto the heel portion 22.

[0070] The sole structure 14 is shown to include one or more selectivelypermeable cushioning devices or membranes 28, which are generallydisposed in the midsole of the sole structure. By way of example, themembranes 28 of the present invention can be formed into products havingvarious geometries such as the plurality of tubular members which arepositioned in a spaced apart, parallel relationship to each other withinthe heel region 22 of the midsole 26 as illustrated in FIGS. 1-3. Thetubular members are sealed to contain an injected captive gas. Thebarrier properties of the membrane 28 are preferably provided by asingle or monolayer embodiment 30A as shown in FIG. 24 or by the layer30 as shown in FIGS. 4-5 which is disposed along the inner surface of athermoplastic outer layer 32. As illustrated in FIGS. 8-18, themembranes 28 of the present invention, whether monolayer or multi-layerembodiments, can be formed into a variety of products having numerousconfigurations or shapes. As should be appreciated at this point,membranes 28 which are formed into cushioning devices employed infootwear may either be fully or partially encapsulated within themidsole or outsole of the footwear.

[0071] Referring again to FIGS. 1-3, a membrane 28 in accordance withteachings of the present invention is illustrated as being in the formof a cushioning device such as those useful as components of footwear.The membrane 28, according to the embodiment illustrated in FIG. 24,comprises a single layer 30A formed from one or more polyester polyolbased urethanes. The polyester polyol based urethanes are preferablyformed by the reaction product of: (a) one or more carboxylic acidshaving six or less carbon atoms with one or more diols having six orless carbon atoms; (b) at least one isocyanate and/or diisocyanate; and(c) optionally, but preferably, one or more extenders. Optionally, thepolyester polyol based urethanes may also employ one or more of thefollowing: (d) hydrolytic stabilizers; (e) plasticizers; (f) fillers;(g) flame retardants; and (h) processing aids. As previously noted, thepolyester polyol is preferably formed as the reaction product of one ormore carboxylic acids with one or more diols, wherein the total numberof carbon atoms contained in the repeating units of polyester polyol inthe reaction product is eight or less. In addition to the one or morediols, the reaction product may also include a relatively small amountof one or more polyfunctional materials such as triols, i.e. no morethan 5.0 equivalent percent based on the total for the reaction productand active hydrogen containing groups.

[0072] Among the carboxylic acids which are considered to be useful informing polyester polyol based urethanes under the present invention,those including adipic, glutaric, succinic, malonic, oxalic and mixturesthereof are considered to be particularly useful.

[0073] Among the diols which are considered to be useful in forming thepolyester polyol based urethanes under the present invention, thoseincluding ethylene glycol, propanediol, butanediol, neopentyldiol,pentanediol and hexanediol and mixtures thereof are considered to beparticularly useful. Among the triols which are considered useful informing the polyester polyol based urethanes are those includingtrimethylol propane are considered to be particularly useful.

[0074] Under preferred embodiments, the polyester polyol basedthermoplastic urethane employed in forming layer 30A for monolayerapplications and 30 for multi-layer applications will include ethyleneglycol adipate. In this regard, certain commercially available ethyleneglycol adipates such as FOMREZ® 22-112 and 22-225 available from WitcoChemical are considered to be useful.

[0075] Among the isocyanates and, more particularly, diisocyanatesemployed in accordance with the teachings of the present invention,those including isophorone diisocyanate (IPDI), methylene bis4-cyclohexyl isocyanate (H₁₂MDI), cyclohexyl diisocyanate (CHDI),hexamethylene diisocyanate (HDI), m-tetramethyl xylene diisocyanate(m-TMXDI), p-tetramethyl xylene diisocyanate (P-TMXDI), and xylylenediisocyanate (XDI) are considered to be useful; particularly useful isdiphenylmethane diisocyanate (MDI). Preferably, the isocyanate(s)employed are proportioned such that the overall ratio of equivalents ofisocyanate to equivalents of active hydrogen containing materials iswithin the range of 0.95:1 to 1.10:1, and more preferably, 0.98:1 to1.04:1. As is known in the urethane chemistry art, the phrase “activehydrogen containing groups” generally refers to groups including aminesand alcohols collectively, which are capable of reacting with theisocyanate groups.

[0076] Optionally, but often preferably, hydrolytic stabilizers will beincluded in the polyester polyol based polyurethanes of the presentinvention. For example, two commercially available carbodiimide basedhydrolytic stabilizers known as STABAXOL P and STABAXOL P-100, which areavailable from Rhein Chemie of Trenton, N.J., have proven to beeffective at reducing the susceptibility of the material to hydrolysis.Still other hydrolytic stabilizers such as those which are carbodiimideor polycarbodiimide based, or based on epoxidized soy bean oil areconsidered useful. The total amount of hydrolytic stabilizer employedwill generally be less than 5.0 wt. % of the composition's total.

[0077] In addition to hydrolytic stabilizers, generally variousplasticizers can be included for purposes of increasing the flexibilityand durability of the final product as well as facilitating theprocessing of the material from a resinous form to a membrane or sheet.By way of example, and without intending to be limiting, plasticizerssuch as those based on butyl benzoyl phthalate have proven to beparticularly useful. Regardless of the plasticizer or mixture ofplasticizers employed, the total amount of plasticizer, if any, willgenerally be less than 40.0 wt. % of the composition's total.

[0078] Fillers may also be employed in the polyester polyol basedpolyurethanes of the present invention, especially with regard tomonolayer applications wherein hydrogen bonding between layers is not aconcern. Included in the class of materials generally referred to hereinas “fillers” are fibrous and particulate materials, non-polar polymericmaterials and inorganic anti-block agents. Examples of such materialsinclude glass and carbon fibers, glass flakes, silicas, calciumcarbonate, clay, mica, talc, carbon black, particulate graphite andmetallic flakes, among others. In the event that fillers are employed,generally the total amount of fillers will be less than 60.0 wt % of thetotal composition weight.

[0079] Yet another class of components which may be employed in thepolyester polyol based urethane compositions of the present inventioninclude flame retardants as the term is understood in the art. While theamount of any flame retardants employed is generally dependent upon thedesired use of the final product, the total amount of flame retardantcontemplated for any application would be 40.0 wt. % or less based onthe total weight of the composition. Among the numerous flame retardantswhich are considered useful, those based on phosphorous or halogenatedcompounds and antimony oxide based compositions are considered to beparticularly useful.

[0080] With regard to the use of additives, otherwise referred to hereinas processing aids, minor amounts of antioxidants, UV stabilizers,thermal stabilizers, light stabilizers, organic anti-block compounds,colorants, fungicides, mold release agents and lubricants as are knownin the art may be employed wherein the total constituency of all suchprocessing aids is generally less than 3.0 wt. %.

[0081] It may also be desirable to include a catalyst in the reactionmixture to prepare the compositions of the present invention. Any of thecatalysts conventionally employed in the art to catalyze the reaction ofan isocyanate with a reactive hydrogen containing compound can beemployed for this purpose; see, for example, Saunders et al.,Polyurethanes, Chemistry and Technology, Part I, Interscience, New York,1963, pages 228-232; see also, Britain et al., J. Applied PolymerScience, 4, 207-211, 1960. Such catalysts include organic and inorganicacid salts of, and organometallic derivatives of, bismuth, lead, tin,iron, antimony, uranium, cadmium, cobalt, thorium, aluminum, mercury,zinc, nickel, cerium, molybdenum, vanadium, copper, manganese andzirconium, as well as phosphines and tertiary organic amines.Representative organotin catalysts are stannous octoate, stannousoleate, dibutyltin dioctoate, dibutyltin dilaurate, and the like.Representative tertiary organic amine catalysts are triethylamine,triethylenediamine, N₁N₁N′₁,N′-tetramethylethylenediamine,N₁N₁N′₁N′-tetraethylethylenediamine, N-methyl-morpholine,N-ethylmorpholine, N₁N₁N′₁,N′-tetramethylguanidine, andN₁N₁N′₁,N′-tetramethyl-1,3-butanediamine.

[0082] Regardless of the catalyst(s) which is utilized, if any, theweight percentage of such material is typically less than one half ofone percent by weight (0.5 wt. %) based on the total weight of thepolyester polyol based thermoplastic urethane reaction mixture.

[0083] Among the extenders which are optionally, but preferably,employed in accordance with the teachings of the present inventions arethose generally selected from the group consisting of alcohols andamines. For example, alcohol based extenders may include ethyleneglycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butanediol,1,6-hexanediol, neopentyl glycol, and the like; and dihydroxyalkylatedaromatic compounds such as the bis (2-hydroxyethyl) ethers ofhydroquinone and resorcinol; p-xylene-α,α′-diol; the bis(2-hydroxyethyl) ether of p-xylene-α,α′-diol; m-xylene-α,α′-diol and thebis (2-hydroxyethyl) ether and mixtures thereof. Illustrative of diamineextenders are aromatic diamines such as p-phenylenediamine,m-phenylenediamine, benzidine, 4,4′-methylenedianiline,4,4′-methylenibis (2-chloroaniline) and the like. Illustrative ofaliphatic diamine extenders is ethylene diamine. Illustrative of aminoalcohols are ethanolamine, propanolamine, butanolamine, and the like.

[0084] Preferred extenders include ethylene glycol, 1,3-propyleneglycol, 1,4-butanediol, 1,6-hexanediol, and the like.

[0085] In addition to the above-described extenders, a small amount oftrifunctional extenders such as trimethylol propane, 1,2,6 hexanetrioland glycerol, may also be present. The amount of trifunctional extendersemployed would preferably be 5.0 equivalent percent or less based on thetotal weight of the reaction product and active hydrogen containinggroups employed.

[0086] Generally, the ratio of polyester polyol to extender can bevaried within a relatively wide range depending largely on the desiredhardness of the final polyurethane elastomer. As such, the equivalentproportion of polyester polyol to extender should be within the range of1:0 to 1:12 and, more preferably, from 1:1 to 1:8.

[0087] In addition to the at least one polyester polyol based urethane,the layer 30A of FIG. 24 may contain one of the following and layer 30of FIGS. 4 and 5 will also preferably contain one or more materialsselected from the group consisting of co-polymers of ethylene and vinylalcohol, polyvinylidene chloride, co-polymers of acrylonitrile andmethyl acrylate, polyethylene terephthalate, aliphatic and aromaticpolyamides, crystalline polymers and polyurethane engineeringthermoplastics. Such materials are preferably blended with the polyesterpolyol based urethane constituent utilizing conventional blendingtechniques prior to forming the membranes.

[0088] For monolayer embodiments 30A, it is preferred that the totalamount of one or more of the above listed materials be up to about 30.0wt. %, since higher amounts tend to result in products which aresomewhat inflexible. In multi-layer embodiments, however, the totalamount of one or more of the above listed materials in a blended layermay be up to about 95.0 wt. %. Thus, for multi-layer constructions,layer 30 which preferably employs blends of at least one polyesterpolyol based urethane and one or more of the above-listed materials willgenerally include up to 70.0 wt. % polyester polyol based thermoplasticurethane but, more preferably, will include between about 1.0 wt. % toabout 50.0 wt. % polyester polyol based thermoplastic urethanes. Underhighly preferred embodiments, the polyester polyol based thermoplasticurethane constituency of the layer 30 will be present in the range ofbetween about 5.0 wt. % to about 25.0 wt. %.

[0089] Of the various materials which are considered to be useful inblended association with the polyester polyol based urethanes,copolymers of ethylene and vinyl alcohol and materials includingmixtures of ethylene-vinyl alcohol copolymers are generally preferred.

[0090] Commercially available products based on copolymers of ethyleneand vinyl alcohol such as SOARNOL™ which is available from the NipponGohsei Co., Ltd. (U.S.A.) of New York, N.Y., and EVAL® which isavailable from Eval Company of America, Lisle, Ill. have proven to beuseful. Highly preferred commercially available copolymers of ethyleneand vinyl alcohol such as EVAL® LCF101A will typically have an averageethylene content of between about 25 mol % to about 48 mol %.

[0091] Other materials useful for blending with one or more polyesterpolyol based urethanes as described above which are commerciallyavailable include BAREX™ 210 which is a copolymer of acrylonitrile andmethyl acrylate available from the British Petroleum Co. and ISOPLAST™which is a polyurethane engineering thermoplastic available from the DowChemical Co.

[0092] In addition to blending the materials selected from the groupconsisting of co-polymers of ethylene and vinyl alcohol, polyvinylidenechloride, co-polymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, aliphatic and aromatic polyamides, crystalline polymersand polyurethane engineering thermoplastics with polyester polyol basedurethanes as described above, it should be recognized by those skilledin the art that such materials can be utilized for the production ofseparate layers for lamination in multi-layer embodiments as describedherein.

[0093] While it is generally preferred that the polyurethanes employedfor both the monolayer and multi-layer embodiments are based on aromaticisocyanates such as diphenylmethane diisocyanate (MDI), in certainmulti-layer constructions, it may be desirable to use aliphaticpolyurethanes in combination with the above described barrier materials.More particularly, polyurethanes based on aliphatic isocyanates wouldpreferably be employed where it is contemplated that aromaticisocyanates beyond a certain concentration would react with the barriermaterial employed. For example, and without intending to be limiting,when a blended layer includes a concentration of 5.0 wt. % of copolymersof ethylene and vinyl alcohol, polyurethanes based on aliphaticisocyanates would be preferred. It may, however, be beneficial toinclude a relatively small amount of at least one aromatic thermoplasticpolyurethane (i.e. those derived from aromatic isocyanates) as aviscosity modifier. Thus, the preferred composition of a blended layerincluding at least 5 wt. % of at least one co-polymer of a reactivebarrier material such as a co-polymer of ethylene and vinyl alcohol canbe summarized as including: (a) at least 50 wt. % of at least onebarrier material selected from the group consisting of co-polymers ofethylene and vinyl alcohol, polyvinylidene chloride, co-polymers ofacrylonitrile and methyl acrylate, polyethylene terephthalate, aliphaticand aromatic polyamides, crystalline polymers and polyurethaneengineering thermoplastics; (b) 1 wt. % to about 50 wt. % of at leastone aliphatic thermoplastic urethane; and (c) up to about 3 wt. % ofaromatic thermoplastic urethanes, wherein the total constituency of theblended layer is equal to 100 wt. %. The aromatic thermoplasticurethanes are also typically selected from the group consisting ofpolyester, polyether, polycaprolactone, polyoxypropylene andpolycarbonate macroglycol based materials and mixtures thereof.

[0094] Additionally, it may be desirable under certain applications toinclude blends of polyurethanes to form layers 30A and 30, respectively,such as where susceptibility to hydrolysis is of particular concern. Forexample, a polyurethane including soft segments of polyether polyols orpolyester polyols formed from the reaction mixture of a carboxylic acidand a diol wherein the repeating units of the reaction product has morethan eight carbon atoms can be blended with polyurethanes includingpolyester polyols having eight or less carbon atoms. Preferably, thepolyurethanes other than those including polyester polyol repeatingunits having eight or less carbon atoms will be present in the blends inan amount up to about 30 wt. %, (i.e. 70.0 wt. % polyethylene glycoladipate based urethane 30.0% isophthalate polyester polyol basedurethane). Specific examples of the polyester polyols wherein thereaction product has more than eight carbon atoms include poly(ethyleneglycol isophthalate), poly(1,4 butanediol isophthalate) and poly(1,6hexanediol isophthalate).

[0095] Additionally, rather than using blends of various thermoplasticurethanes, it is also possible to utilize a single polyurethane whereinvarious soft segments are included therein. Again, without intending tobe limiting, the soft segments may include, in addition to soft segmentshaving a total of eight carbon atoms or less, polyether polyols,polyester polyols having a total of more than eight carbon atoms, ormixtures thereof. It is contemplated that the total amount of softsegment constituency which includes the reaction product of a carboxylicacid and a diol having a total carbon atom count of more than eight, bepresent in an amount of up to about 30 wt. % of the total weight of softsegments included in the polyurethane. Thus, at least 70 wt. % of thesoft segment repeating units will be the reaction products of carboxylicacid and a diol, wherein the total carbon atom count for the reactionproduct is eight or less.

[0096] It should also be noted that there are a number of ways to addpolyurethanes with up to 30 wt. % of polyesters with repeat unitscontaining more than eight carbon atoms to the polyurethanes of thisinvention. Thirty percent or less of a polyurethane derived frompolyester polyols containing repeat units with more than eight carbonscan be blended as finished polymers with 70 wt. % or more ofpolyurethanes derived from polyester polyols with repeat unitscontaining eight or less carbon atoms, or a single polyurethane could beprepared from a mixture of polyester polyols wherein 70 wt. % or morecontain repeat units with eight carbons or less and the balance containsrepeat units with more than eight carbons as described previously. Apolyurethane could be prepared from a single polyol prepared by reactionfrom dicarboxylic acids and diols such that 70 wt. % of the repeat unitsin the polyester polyol contain eight or less carbon atoms. Combinationsof these techniques are also possible. Among the acids that contain morethan six carbon atoms that could be employed are isophthalic andphthalic acids.

[0097] As discussed, the membranes 28 of the present invention may alsobe in the form of multi-layer constructions. For example, membranes 28and A of FIGS. 4-7 include a layer 32 formed of a flexible resilientelastomeric material which preferably is resistant to expansion beyond apredetermined maximum volume when the membrane is subjected to gaseouspressure.

[0098] The layer 32 preferably is formed of a material or combination ofmaterials which offer superior heat sealing properties, flexural fatiguestrength, a suitable modulus of elasticity, tensile and tear strengthand abrasion resistance. Among the available materials which offer thesecharacteristics, it has been found that thermoplastic elastomers of theurethane variety, otherwise referred to herein as thermoplasticurethanes or simply TPU's, are highly preferred because of theirexcellent processability.

[0099] Among the numerous thermoplastic urethanes which are useful informing the outer layer 32, urethanes such as PELLETHANE™ 2355-ATP,2355-95AE and 2355-85A (trademarked products of the Dow Chemical Companyof Midland, Mich.), ELASTOLLAN® (a registered trademark of the BASFCorporation) and ESTANE® (a registered trademark of the B.F. GoodrichCo.), all of which are either ester or ether based, have proven to beparticularly useful. Still other thermoplastic urethanes based onpolyesters, polyethers, polycaprolactone and polycarbonate macroglycolscan be employed. Further, in addition to the commercially availablepolyurethanes, it should also be noted that layer 32 of FIG. 4 andlayers 32 and 34 of membrane A shown in FIG. 7 could also be made fromthe polyester polyol based polyurethanes containing soft segmentswherein the reaction product has eight or less carbon atoms. This wouldgenerally result in a reduction in GTR's since much of the resistance togas diffusion in multi-layer constructions comes from the barrier layer.

[0100] As previously noted, the membranes as disclosed herein can beformed by various processing techniques including but not limited toextrusion, blow molding, injection molding, vacuum molding and heatsealing or RF welding of tubing and sheet extruded film materials. Withregard to the multi-layer membranes described herein, such membranes aremade from films formed by co-extruding the material forming layer 30together with the material comprising layer 32. After forming themulti-layered film materials, the film materials are heat sealed orwelded by RF welding to form the inflatable membranes which are highlyflexible in nature.

[0101] The membranes, whether in the form of sheet, substantially closedcontainers, cushioning devices, accumulators or other structures,preferably will have a tensile strength on the order of at least about2500 psi; a 100% tensile modulus of between about 350-3000 psi and/or anelongation of at least about 250% to about 700%.

[0102] Referring now to FIGS. 6 and 7, an alternative membraneembodiment A in the form of an elongated tubular shaped multi-layeredcomponent is illustrated. The modified membrane A is essentially thesame as the membrane 28 illustrated in FIGS. 4 and 5 except that a thirdlayer 34 is provided contiguously along the inner surface of the layer30, such that layer 30 is sandwiched between an outer layer 32 and aninnermost layer 34. The innermost layer 34 is also preferably made froma thermoplastic urethane material. In addition to the perceived benefitof enhanced protection against degradation of layer 30, layer 34 alsotends to assist in providing for high quality welds which facilitate theformation of three-dimensional shapes for products such as cushioningdevices useful in footwear.

[0103] Membranes such as those shown in FIGS. 1-7 and FIG. 24 arepreferably fabricated from extruded tubes. Lengths of the tubing whichtypically range from about one foot up to about five feet in length.Membranes can then be inflated to a desired initial inflation pressureranging from 0 psi ambient to 100 psi, preferably in the range of 5 to50 psi, with the captive gas preferably being nitrogen. Sections of thetubing are thereafter RF welded or heat sealed to the desired lengths.The individual membranes produced upon RF welding or heat sealing arethen separated by cutting through the welded areas between adjacentmembranes. It should also be noted that the membranes can be fabricatedfrom so-called flat extruded tubing as is known in the art whereby theinternal geometry is welded into the tube.

[0104] With regard to extruding the multi-layer embodiments describedherein, as the material which forms layers 30, 32 and optionally, layer34 advance to the exit end of the extruder through individual flowchannels, once they near the die-lip exit, the melt streams are combinedand arranged to float together in layers typically moving in a laminarflow as they enter the die body. Preferably, the materials are combinedat a temperature of between about 300° F. to about 465° F. and apressure of at least about 200 psi to obtain optimal wetting for maximumadhesion between the contiguous portions of the layers 30, 32 and 34respectively and further to enhance hydrogen bonding between the layerswherein the materials employed are conducive to hydrogen bonding. Again,for multi-layered laminates, it is preferred that the polyester polyolsutilized in the polyurethanes of layers 30, 32 and 34 be highlyaliphatic in nature, since aliphatic urethanes have been found to bereadily processable utilizing conventional techniques such as sheetextrusion.

[0105] To this end, it is believed that hydrogen bonding occurs betweenthe respective layers as the result of available functional groups withhydrogen atoms that can participate in hydrogen bonding such as hydrogenatoms in hydroxyl groups or hydrogen atoms attached to nitrogen atoms inurethane groups and various receptor groups such as oxygen atoms inhydroxyl groups, carbonyl oxygens in urethane groups and ester groupsand chlorine atoms in PVDC, for example.

[0106] The chemical reaction provided below illustrates the theoreticalsurface bond which is believed to occur between layers 32 and 34 withlayer 30 across substantially the entire intended contact surface areaof the membrane:

[0107] In addition to the hydrogen bonding as illustrated above, to amore limited extent, it is believed that a certain amount of covalentbonds are formed between the second and third layers 32 and 34,respectively, with the first layer 30. Still other factors such asorientation forces and induction forces, otherwise known as van derWaals forces, which result from London forces existing between any twomolecules and dipole-dipole forces which are present between polarmolecules are believed to contribute to the bond strength betweencontiguous layers of thermoplastic urethane and the main layer.

[0108] The hydrogen bonding as described above is in contrast to priorart embodiments which, failing to recognize the existence and/orpotential of such bonding, typically have required the use of adhesivetie-layers such as Bynel®, for example, to maintain the bonding betweenthe various layers.

[0109] As noted above, since fillers tend to negatively effect theso-called hydrogen bonding capacity of multi-layer embodiments, whilethe use of up to about 60.0 wt. % of fillers in monolayer embodiments iscontemplated, the use of fillers in processing multi-layer membraneswhere hydrogen bonding is desired should be limited, if used at all.

[0110] Referring to FIGS. 12-16, membranes in the form of air bladdersare fabricated by blow molding are shown. To form the bladders, singlelayer parisons are extruded or parisons of two layer or three layer filmare co-extruded as illustrated in FIGS. 21-23. Thereafter, the parisonsare blown and formed using conventional blow molding techniques. Theresulting bladders, examples of which are shown in FIGS. 12 and 15, arethen inflated with the desired captive gas to the preferred initialinflation pressure and then the inflation port (e.g. inflation port 38)is sealed by RF welding.

[0111] Still other embodiments formed from the membranes describedherein are shown in FIGS. 8-10. Sheets or films of extruded monolayerfilm or co-extruded two layer or three layer film are formed to thedesired thicknesses. For example, the thickness range of the co-extrudedsheets or films is preferably between 0.5 mils to 10 mils for the layer30 and between 4.5 mils to about 100 mils for the layers 32 and 34,respectively. For monolayer cushioning device embodiments, the averagethickness will generally be between 5 mils to about 60 mils and, morepreferably, between about 15 mils and to about 40 mils.

[0112] Still another embodiment formed from a membrane of the presentinvention is shown in FIGS. 17 and 18. The air bladder is fabricated byforming extruded single layer or co-extruded multiple layer tubinghaving a desired thickness range. The tubing is collapsed to a lay flatconfiguration and the opposite walls are welded together at selectedpoints and at each end using conventional heat sealing or RF weldingtechniques. The cushioning device is then inflated through a formedinflation port 38 to the desired inflation pressure which ranges from 0psi ambient to 100 psi, and preferably from 5 to 50 psi, with a captivegas such as nitrogen.

[0113] In addition to employing the membranes of the present inventionas cushioning devices or air bladders as described above, still anotherhighly desirable application for the membranes of the present inventionis for accumulators as illustrated in FIGS. 19, 20 and 25.

[0114] Referring to FIG. 25, there is shown an accumulator embodimentformed from a monolayer membrane as described above. Likewise, referringto FIGS. 19 and 20, there are shown two alternative accumulatorembodiments formed from a multi-layer membrane of the present invention.Accumulators, and more particularly, hydraulic accumulators are used forvehicle suspension systems, vehicle brake systems, industrial hydraulicaccumulators or for other applications having differential pressuresbetween two potentially dissimilar fluid media. The membrane 124separates the hydraulic accumulator into two chambers or compartments,one of which contains a gas such as nitrogen and the other one of whichcontains a liquid. Membrane 124 includes an annular collar 126 and aflexible body portion 128. Annular collar 126 is adapted to be securedcircumferentially to the interior surface of the spherical accumulatorsuch that body portion 128 divides the accumulator into two separatechambers. The flexible body portion 128 moves generally diametricallywithin the spherical accumulator and its position at any given time isdependant upon the pressure of the gas on one side in conjunction withthe pressure of the liquid on the opposite side.

[0115] By way of further example, FIG. 20 illustrates a product in theform of a hydraulic accumulator including a first layer 114 made fromthe materials described with reference to layers 30A and 30 as describedabove. Additionally, the product includes layers 112 and 116 formed fromone or more thermoplastic urethanes, one or more barrier materials or acombination of at least one urethane and barrier material as describedwith reference to layers 32 and 34 above. As shown, the first layer 114only extends along a segment of the entire accumulator body portion. Itmay be desirable to utilize such embodiments, otherwise referred toherein as “intermittent constructions” under circumstances where thedelamination potential along certain segments of a product is greatest.One such location is along the annular collar 126 of the bladder ordiaphragm for hydraulic accumulators in multi-layer embodiments. Thus,while the multi-layer membranes of the present invention are generallymore resistant to delamination and do a better job of preventing gasfrom escaping along interfaces between layers such as those occurringalong the annular collar via capillary action, it should be recognizedthat the membranes 110 described herein can include segments which donot include layer 114.

[0116] To form the membranes 110 which are subsequently formed into theproducts illustrated in FIGS. 19, 20 and 25, a number of differentprocesses can be used, including but not limited to, extrusion andco-extrusion blow molding utilizing continuous extrusion, intermittentextrusion utilizing (1) reciprocating screw systems; (2) ramaccumulator-type systems; and (3) accumulator head systems, co-injectionstretch blow molding, extruded or co-extruded sheet, blown film, tubingor profiles. With regard to multi-layer processes, it has been foundthat utilizing co-extrusions give rise to products which appear todemonstrate the above desired hydrogen bonding between the respectivelayers 114 and, 112 and 116, respectively, when conducive materials areutilized. To form a product such as a hydraulic accumulator bladder ordiaphragm via a multi-layer process, such as blow molding, any one of anumber of commercially available blow molding machines such as a BekumBM502 utilizing a co-extrusion head model No. BKB95-3B1 (not shown) or aKrup KEB-5 model utilizing a model No. VW60/35 co-extrusion head (notshown) could be utilized.

[0117] As previously noted, the manufacture of monolayer membranesgenerally resembles the manufacture of multi-layer membranes butrequires far fewer process controls. For example, monolayer membranesrequire only a single extruder with no feed block being required. Sheetcan be made by forcing molten polymer formed in the extruder through acoat hanger die. Collapsed tubing and parisons used in blow molding aremade by forcing molten plastic generated by an extruder through anannular die.

[0118] A brief description of preferred multi-layer processingtechniques will now be provided. Initially, the resinous materials to beextruded are first dried to the manufacturer's specification (ifnecessary) and fed into the extruder. Typically, the materials are fedinto the extruders according to the order in which the layers are to bearranged. For example, with regard to a three layer embodiment, amaterial including polyester polyol based urethane is fed to an outsideextruder, a material such as a TPU and/or one or more barrier materialsis fed to a middle extruder and a material such as a TPU is fed to aninside extruder. The extruder heat profile is set for the bestprocessing of the individual materials. It is suggested, however, thatno more than a 20° F. difference be present at the exit point of eachextruder. As the material is forced forward in each extruder, the heatprofile is set to achieve the best molten mass. The heat profile wouldtypically be set for between 300° F. to about 465° F. with the feed zonebeing the lowest set point and all other set points gradually increasingin increments of approximately 10° F. until the desired melt isachieved. Once leaving the extruders a section of pipes is sometimesused to direct the material to the multi-layered head (i.e. three ormore heads). It is at this point that any adjustments for differences inheat are addressed. The pumping action of the extruders not only forcesthe material into the individual head channels or flow paths but alsodetermines the thickness of each layer. As an example, if the firstextruder has a 60 mm diameter, the second extruder has a 35 mm diameterand the third extruder has a 35 mm diameter, the speeds required toproduce a 1.3 liter bladder or diaphragm requiring 2 mm for the outsidelayer, 3 mils for the middle layer and 2 mm for the inside layer for thevarious extruder would be approximately 26 seconds for the firstextruder having a screw speed of about 10 rpm's, the second extruderwould have a screw speed of about 5 rpm's and the third extruder wouldhave a screw speed of about 30 rpm. Once the materials enter the headchannels or flow paths, the heat would normally be held constant or bedecreased to adjust for the melt strength of the materials. Theindividual head channels or flow paths keep separate the molten masseswhile directing them downward and into the shape of a parison.

[0119] Just prior to entering the lower die or bushing and the lowermandrel, the material head channels or flow paths are brought togetherunder the pressure created by the now unitary flow path surface area,the gap between the lower bushing and mandril and the pressure on theindividual layers from the respective extruders. This pressure must beat least 200 psi and is normally, under the conditions described, inexcess of 800 psi. At the point where the materials come together, oneparison is now formed that is a laminate made up of the three layers.The upper limit of the pressure is essentially only constrained by thephysical strength of the head. After exiting the head, the laminate isclosed on each end by the two mold halves and a gas such as air isinjected into the mold forcing the laminated parison to blow up againstthe mold and be held in this fashion until sufficient cooling has takenplace (i.e. approximately 16 seconds for the aforementioned sample), atwhich point the gas is exhausted. The part is then removed from the moldand further cooling is allowed for sufficient time to allow for the partto be de-flashed or further processed as some parts may require. Asshould now be understood by those skilled in the art, the layers must beheld separate until fully melted and preformed into a hollow tube atwhich time they are bonded together under the heat and pressuredescribed herein.

[0120] As those skilled in the plastic forming industry will recognize,the three major components of a blow molding machine, namely theextruders, die heads and mold clamps, come in a number of differentsizes and arrangements to accommodate for the consumer production rateschedule and size requirements.

[0121] A multi-layer process known as sheet co-extrusion is also auseful technique to form membranes in accordance with the teachings ofthe present invention. Sheet co-extrusion generally involves thesimultaneous extrusion of two or more polymeric materials through asingle die where the materials are joined together such that they formdistinct, well bonded layers forming a single extruded product.

[0122] The equipment required to produce co-extruded sheet consists ofone extruder for each type of resin which are connected to aco-extrusion feed block such as that shown in FIGS. 21 and 23, which arecommercially available from a number of different sources including theCloreon Company of Orange, Tex. and Production Components, Inc. of EauClaire, Wis., among others.

[0123] The co-extrusion feed block 150 consists of three sections. Thefirst section 152 is the feed port section which connects to theindividual extruders and ports the individual round streams of resin tothe programming section 154. The programming section 154 then reformseach stream of resin into a rectangular shape the size of which is inproportion to the individual desired layer thickness. The transitionsection 156 combines the separate individual rectangular layers into onesquare port. The melt temperature of each of the TPU layers shouldgenerally be between about 300° F. to about 465° F. To optimize adhesionbetween the respective layers, the actual temperature of each meltstream should be set such that the viscosities of each melt streamclosely match. The combined laminar melt streams are then formed into asingle rectangular extruded melt in the sheet die 158 which preferablyhas a “coat hanger” design as shown in FIG. 22 which is now commonlyused in the plastics forming industry. Thereafter the extrudate can becooled utilizing rollers 160 forming a rigid sheet by either the castingor calendaring process.

[0124] Similar to sheet extrusion, the equipment required to produceco-extruded tubing consists of one extruder for each type of resin witheach extruder being connected to a common multi-manifolded tubing die.The melt from each extruder enters a die manifold such as the oneillustrated in FIG. 23 which is commercially available from a number ofdifferent sources including Canterberry Engineering, Inc. of Atlanta,Ga. and Genca Corporation of Clearwater, Fla. among others, and flows inseparate circular flow channels 172A and 172B for the different melts.The flow channels are then shaped into a circular annulus the size ofwhich is proportional to the desired thickness for each layer. Theindividual melts are then combined to form one common melt stream justprior to the die entrance 174. The melt then flows through a channel 176formed by the annulus between the outer surface 178 of a cylindricalmandrel 180 and the inner surface 182 of a cylindrical die shell 184.The tubular shaped extrudate exits the die shell and then can be cooledinto the shape of a tube by many conventional pipe or tubing calibrationmethods. While a two component tube has been shown in FIG. 23 it shouldbe understood by those skilled in the art that additional layers can beadded through separate flow channels.

[0125] Regardless of the plastic forming process used, it is desirablethat a consistent melt of the materials employed be obtained toaccomplish bonding between layers across the intended length or segmentof the laminated product. Again then, the multi-layer processes utilizedshould be carried out at maintained temperatures of from about 300° F.to about 465° F. Furthermore, it is important to maintain sufficientpressure of at least 200 psi at the point where the layers are joinedwherein the above described hydrogen bonding is to be effectuated.

[0126] As previously noted, in addition to the excellent bonding whichcan be achieved for the laminated membrane embodiments of the presentinvention, another objective, especially with regard to membranesemployed as cushioning devices for footwear, is to provide membraneswhich are capable of retaining captive gases for extended periods oftime. In general, membranes which offer gas transmission rate values of15.0 or less for nitrogen gas as measured according to the proceduresdesignated at ASTM D-1434-82 for membranes having an average thicknessof 20 mils are acceptable candidates for extended life applications.Thus, while the membranes of the present invention can have varyingthicknesses depending mainly on the intended use of the final product,the membranes of the present invention will preferably have a gastransmission rate value of 15.0 or less when normalized to a thicknessof 20 mils regardless of the actual thickness of the membrane. Likewise,while nitrogen gas is the preferred captive gas for many embodiments andserves as a benchmark for analyzing gas transmission rates in accordancewith ASTM D-1434-82, the membranes can contain a variety of differentgases and/or liquids.

[0127] In this regard, because of the excellent characteristics offeredby the polyester polyol based urethanes in terms of flexibility,resistance to degradation caused by moisture and resistance to undesiredgas transmissions, among others, the membranes of the present inventioncan be employed as either monolayer or multi-layer embodiments. Underpreferred embodiments, the membranes of the present invention will havea gas transmission rate of 10.0 and still, more preferably, will havegas transmission rates of 7.5 or less for nitrogen gas at 20 mils. Stillmore preferably, the membranes of the present invention will have a gastransmission rate of 5.0 or less and, still more preferably yet, willhave a gas transmission rate of 2.5 or less for nitrogen gas at 20 mils.Under the most highly preferred embodiments, the membranes of thepresent invention will have a gas transmission rate of 2.0 or less fornitrogen gas for membranes having an average thickness of 20 mils.

[0128] To prepare Samples 1-12 as set forth in Table I for gastransmission rate analysis, the polyester polyol based urethane wasinitially prepared by adding one or more of the following constituentsto a 2000 ml reaction flask: (1) polyester polyol (i.e. commercialproduct or reaction product of dicarboxylic acid and diol, asdescribed); (2) difunctional extender; and (3) processing aids such aswaxes and antioxidants. Thereafter, the hydroxyl component was heated tobetween approximately 95° C.-115° C. (depending on the composition) andstirred to dissolve and homogenize the constituents. Subsequently, avacuum of less than 0.2 mm Hg was applied under constant stirring tocontrol foaming. After foaming was completed, the flask was degassed forapproximately 30 minutes until virtually all bubbling ceased.

[0129] Next, the isocyanate component was prepared by disposing adiisocyanate in a 250 ml polypropylene beaker and placing thediisocyanate in an oven heated to between approximately 50-65° C. Uponobtaining a temperature of between about 50-65° C., the desired amountof the isocyanate constituent was weighted out and the catalyst, if any,was added to the isocyanate constituent under constant mixing.

[0130] Once the catalyst was fully mixed in, the desired amount ofhydroxyl component was added to the isocyanate component to effectuatepolymerization. As polymerization began and the viscosity increased(generally between about 7-12 seconds after addition), the reactionproduct was poured into pans coated with a desirable release agent andallowed to fully cool. Upon cooling, the newly formed polymer was cutinto granules and dried for approximately 2-4 hours at between 85-100°C. Thereafter, Samples 1-10, as set forth in Table I, were prepared bycompression molding granules of plastic into sheets to conduct analysisrelating to gas transmission properties.

[0131] With regard to Sample 11 as illustrated in Table I, after formingthe polyester polyol based urethane as described above, 70.0 wt. % ofthe material was blended and extruded along with the 30.0 wt. % BAREX™210 available from BP Chemical, Inc., at a temperature of approximately420° F. to provide a blended sample for gas transmission analysis.Further, with regard to Sample 12, a membrane was formed for gastransmission analysis by blending 70.0 wt. % of the polyester polyolbased urethane set forth in Sample 12 with 30.0 wt. % of the BAREX™ 210at a temperature of approximately 420° F. TABLE 1 Gas Transmission RatesFor Single Layers Formulation 1 2 3 4 5 6 7 8 9 10 11 12 13 14Polybutanediol Adipate (a) 2000 m.w.¹ 43.12 (b) 700 m.w.² 15.09 EthyleneGlycol Adipate (a) 1000 m.w.³ 61.11 62.29 49.18 60.83 49.60 30.26 16.3942.84 51.23 (b) 500 m.w.⁴ 22.69 32.77 HD Adipate / HD Isophthalate (a)1000 m.w.⁵ 18.36 Ethylene Glycol Glutarate (a) 1000 m.w.⁶ 51.23 EthyleneGlycol 4.25 Dipropylene glycol 0.58 Butyl Carbitol 0.21 0.25 0.25 1,4Butanediol 7.37 6.05 9.96 6.00 8.93 6.81 7.37 9.22 6.06 9.22 H12MDI⁷41.07 39.84 MDI⁸ 33.04 32.5 40.52 43.15 38.96 32.40 38.96 MDI/IIq.MDI⁹33.12 33.03 Irganaox 1010¹⁰ 0.125 0.15 0.15 0.15 0.15 0.15 0.15 0.150.15 0.15 0.15 Advawax 280¹¹ 0.125 0.15 0.15 0.15 0.15 0.15 0.15 0.150.15 Wax¹² 0.30 0.15 Catalyst¹³ 0.04 0.04 0.04 0.04 0.04 0.10 0.10 0.020.04 0.04 0.04 Kemamide W-40¹⁴ 0.15 Pellethane 2355-85 ATP¹⁵ 100.0 100.0Pellethane 2355-95 AE¹⁶ 100.0 Total Wt. % 100.0 100.0 100.0 100.0 100.0100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

[0132] TABLE II GTR (cc/m² * atm * day) Sample Average Normalized to 20mils Number Thickness GTR (cc/m² * atm * day) thickness 1 16.25 mils30.95 25.15 2 15.2 mils  11.71 8.9 3 17.13 mils 9.13 7.82 4 18.49 mils6.58 6.08 5 17.54 mils 7.07 6.19 6 19.93 mils 9.22 9.19 7 19.93 mils6.19 6.17 8 18.31 mils 1.20 1.10 9 16.93 mils 3.47 2.93 10 14.47 mils17.92 12.96 11 19.22 mils 1.24 1.19 12 17.1 mils  2.73 2.33 13 19.95mils 36.42 36.33 14 18.25 mils 24.12 22.01

[0133] As illustrated in Table II, each of the Samples 2-12 demonstratedbetter gas transmission rate results than the control Samples 13-14,which were formed of commercially available thermoplastic urethaneresins. Each of the samples, namely Samples 2-10 which relate topolyethylene glycol adipate and ethylene glycol glutarate basedurethanes and Samples 11-12 which relate to polyethylene glycol adipatebased urethane blends, including BAREX™ 210, generally demonstratedbetter gas transmission rate values than the polybutanediol adipatebased urethane of Sample 1. As illustrated, each of the Samples 2-12,exhibited a gas transmission rate of less than 15.0 for N₂ at 20 mils.

[0134] A multi-layer sample was also prepared by laminating two layersof the polyester polyol based urethane as set forth in Sample 11 ofTable I along with a third layer of commercially available materialknown as ISOPLAST™. To laminate the multi-layer sample, a sheet of 5 milISOPLAST™ film was sandwiched between two layers of the polyester polyolbased urethane, each having a thickness of 19 mils. The multi-layersample was then pressed within a hydraulic press having upper and lowerplatens heated to about 420° F. The films were pressed together at apressure of about 2,000 psig to give rise to a sample having an overallthickness of approximately 18.25 mils.

[0135] Upon conducting the gas transmission rate analysis on themulti-layer sample, it was discovered that the sample had a GTR of 8.87for nitrogen at 18.25 mils and as normalized to 20.0 mils had a GTR of8.09. Thus, the multi-layer sample also met the objective of a gastransmission rate of less than 15.0.

[0136] Finally, in addition to the monolayer and multi-layer membranesamples as set forth above, a thermoset version of a polyester polyolbased urethane was also prepared and analyzed for gas transmission.

[0137] The sample, as set forth in Table III below, was prepared bydehydrating and degassing the polyester polyol under a vacuum for twohours at 100° C. and cooled to 60° C. at which time the catalyst wasadded. Concurrently, the Isonate™ 2143L was heated to 45° C. anddegassed for twenty minutes before its addition to the polyestercomponent. The polyester polyol and polyisocyanate were then mixed andstirred carefully in a polypropylene beaker to avoid the introduction ofair. Upon mixing, the mixture was cast into a warm plaque mold where itwas allowed to cure for two hours at ambient temperature and pressurebefore demolding. The resulting membrane was allowed to remain atambient conditions for seven days prior to testing. TABLE III Ethyleneglycol adipate 77.36 (a) 1000 m.w.¹ MDI² 22.34 Catalyst³ 0.30 100.0

[0138] The thermoset version of the polyester polyol based urethanes asset forth in Table III exhibited a gas transmission rate of 3.07 for a73 mils thickness. Upon normalizing, the gas transmission rate wascalculated to be 11.2 for N₂based on a 20 mil thickness. Thus, boththermoplastic and thermoset materials appear to be useful in accordancewith the teachings of the present invention.

[0139] In addition to the improved resistance to gas transmissionoffered by the various products formed from the polyester polyol basedurethanes described herein, products made from polyester polyol basedurethanes have also shown a marked improvement in durability overthermoplastic urethanes which do not include polyester polyols.

[0140] For example, as illustrated in Table IV below, multiple sampleswere prepared and analyzed for durability utilizing a test method knownas as a KIM test. In accordance with the KIM test procedures, two sheetswere extruded from differing materials with each sheet being formed intoidentically shaped cushioning device components having an average wallthickness of 18 mils. The material utilized for the Set A cushioningdevices is the same as that set forth in Table I as Formulation No. 11.The Set B cushioning devices were made from a material such asPellethane 2355-85A, a thermoplastic urethane that does not contain anypolyethylene glycol adipate soft segments.

[0141] Upon inflating the cushioning devices to 20.0 psig with nitrogengas, each sample was intermittently compressed by a reciprocating pistonhaving a 4.0 inch diameter platen. The stroke of each piston wascalibrated to travel a height which would compress each sample to anaverage of 25.0% of the initial inflated height at maximum stroke. Thereciprocating pistons were then allowed to cycle or stroke until a partfailure was detected. Part failure, as the term is used herein, isdefined as a sufficient leakage of the nitrogen gas and deflation of thecushioning device to cause a lever placed in identical locations alongeach of the cushioning devices to contact a microswitch which stops thereciprocating piston stroke. The total number of cycles or strokes werethen recorded for each sample with a high number of strokes beingindicative of a more durable material. Preferably, permanently inflatedcushioning devices should be capable of withstanding at least about200,000 cycles to be considered for applications as footwear components.

[0142] As can be seen from a review of Table IV, the cushioning devicesof Set A formed from the polyester polyol based urethane outperformedthe cushioning devices formed from the aromatic thermoplastic basedurethane of Set B by over three times as many cycles. Thus, thepolyester polyol based urethanes utilized under the present inventionnot only offer better resistance to undesired gas transmission, but alsohave been shown to offer enhanced durability over thermoplasticurethanes which do not include polyester polyol soft segments havingeight or less carbon atoms having eight or less carbon atoms in therepeating units. TABLE IV Sample No. Avg No. of Cycle Set A* 754,111 SetB** 217,797

[0143] In addition to a high degree of durability, it is often desirableto form products which are relatively transparent in nature, i.e.products which meet certain standards in terms of the yellowness leveldetected and the transmission of light through the material. Forexample, transparency of the product is often a consideration forcushioning devices such as those utilized as components of footwearwherein the cushioning device is visually accessible.

[0144] In this regard, cushioning devices formed from Pellethane 2355-87ATP, an aromatic thermoplastic based urethane, have proven to be usefulfor shoe components since the material has been shown to offeracceptable levels both in terms of the yellowness level detected and thelight transmission through the material. Thus, polyester polyol basedurethanes would preferably have similar and, more preferably, improvedtransparency characteristics as compared to aromatic thermoplasticurethanes such as Pellethane 2355-87ATP, among others.

[0145] Samples of both Pellethane 2355-87ATP and a polyester polyolbased urethane including: 50.96 wt. % FOMREZ 22-122 (1000 m.w.); 9.11wt. % 1,4 Butanediol; 38.81 wt. % ISONATE 2125M; 0.50 wt. % IRGANOX1010; 0.15 wt. % ADVAWAX 280; 0.30 wt. % montan ester wax; and 0.02 wt.% catalyst, were prepared by extruding smooth sided, collapsed tubeshaving an average wall thickness of 32 mils. Each sample was thereafteranalyzed for its yellowness index and the total transmission of lighttherethrough utilizing a Hunter Lab Color QUEST™ Spectocolorimeter inaccordance with the instrument's instruction manual.

[0146] The yellowness index readings were standardized in the {rsin}mode, and readings were taken along the reflectance port. The totaltransmission measurements were also standardized and the measurementswere taken by readings without glass slides along the transmissionports.

[0147] The Pellethane 2355-87ATP had a yellowness index of 4.00 and atotal transmission of light of 90.85% based on a maximum value of 100.0%transmission. The polyester polyol based urethane had a yellowness indexof 1.52 and a total transmission of light of 91.75%. The polyesterpolyol based urethanes, thus, not only appear to be more durable thanaromatic thermoplastic based urethanes but also appear to offer bettervalues both in terms of a lower yellowness index and a higher lighttransmission. This improvement in terms of both decreased yellowness andan increased transmission of light should enhance the aestheticcharacteristics of many final products.

[0148] While the above detailed description describes the preferredembodiment of the present invention, it should be understood that thepresent invention is susceptible to modification, variation andalteration without deviating from the scope and fair meaning of thesubjoined claims.

What is claimed is:
 1. A membrane comprising: a polyurethane including apolyester polyol, said membrane having a gas transmission rate of 15.0or less for nitrogen gas wherein said membrane has an average thicknessof approximately 20.0 mils.
 2. The membrane according to claim 1,wherein said polyester polyol of said polyurethane is selected from thegroup consisting of the reaction product of (a) a carboxylic acid havingsix or less carbon atoms and (b) a diol having six or less carbon atoms,wherein the repeating units of the polyester polyol formed by theaforesaid reaction has eight carbon atoms or less.
 3. The membraneaccording to claim 2, wherein the carboxylic acid is selected from thegroup consisting of adipic, glutaric, succinic, malonic and oxalicacids, and mixtures thereof.
 4. The membrane according to claim 3,wherein the carboxylic acid employed includes adipic acid.
 5. Themembrane according to claim 2, wherein the diol is selected from thegroup consisting of ethylene glycol, propanediol, butanediol,neopentyldiol, pentanediol, hexanediol and mixtures thereof.
 6. Themembrane according to claim 5, wherein the diol employed includesethylene glycol.
 7. The membrane according to claim 2, wherein saidpolyurethane further comprises at least one extender.
 8. The membraneaccording to claim 7, wherein said extender is selected from the groupconsisting of alcohols and amines.
 9. The membrane according to claim 7,wherein said extender is selected from the group consisting of ethyleneglycol, 1,3 propylene glycol, 1,4-butanediol and 1,6-hexanediol.
 10. Themembrane according to claim 7, wherein said at least one extender andsaid at least one polyester polyol include active hydrogen containinggroups.
 11. The membrane according to claim 7, wherein the ratio ofpolyester polyol to extender is between about 1:0 to about 1:12.
 12. Themembrane according to claim 11, wherein the ratio of polyester polyol toextender is between about 1:1 to about 1:8.
 13. The membrane accordingto claim 10, wherein the ratio of isocyanate contained in saidpolyurethane to active hydrogen containing groups is between about0.95:1 to about 1.10:1.
 14. The membrane according to claim 13, whereinthe ratio of isocyanate to active hydrogen containing groups is betweenabout 0.98:1 to about 1.04:1.
 15. The membrane according to claim 2,further comprising a hydrolytic stabilizer.
 16. The membrane accordingto claim 15, wherein said hydrolytic stabilizer is present in an amountof up to 5.0 wt. %.
 17. The membrane according to claim 15, wherein saidhydrolytic stabilizer is selected from the group consisting ofcarbodiimides, polycarbodiimides and epoxidized soy bean oil.
 18. Themembrane according to claim 2, wherein said polyurethane includes atleast one plasticizer, said plasticizer being present in an amount of upto 40.0 wt. %
 19. The membrane according to claim 2, wherein saidpolyurethane includes at least one flame retardant, said flame retardantbeing present in an amount of up to 40.0 wt. %.
 20. The membraneaccording to claim 2, wherein said polyurethane includes at least onefiller, said filler being present in an amount of up to 60 wt. %. 21.The membrane according to claim 2, wherein at least one additive isemployed, said additive being selected from the group consisting ofantioxidants, ultra-violet stabilizers, thermal stabilizers, lightstabilizers, organic anti-block compounds, colorants, fungicides, moldrelease agents and lubricants, said at least one additive being presentin an amount of up to 3.0 wt. %.
 22. The membrane according to claim 2,further comprising at least one triol.
 23. The membrane according toclaim 22, wherein said at least one triol includes trimethyol propane.24. The membrane according to claim 2, further comprising at least onematerial selected from the group consisting of co-polymers of ethyleneand vinyl alcohol, polyvinylidene chloride, co-polymers of acrylonitrileand methyl acrylate, polyethylene terephthalate, aliphatic and aromaticpolyamides, crystalline polymers and polyurethane engineeringthermoplastics, said material being blended with said polyurethane priorto forming said membrane.
 25. The membrane according to claim 24,wherein said membrane includes up to about 70.0 wt. % polyester polyolbased urethane.
 26. The membrane according to claim 25, wherein saidmembrane includes between about 5.0 wt. % to about 25.0 wt. % polyesterpolyol based urethane.
 27. The membrane according to claim 24, whereinsaid material selected from said group includes at least one copolymerof ethylene and vinyl alcohol.
 28. The membrane according to claim 27,wherein at least one of the copolymers of ethylene and vinyl alcohol hasan ethylene content of between about 25 mol. % to about 48 mol. %. 29.The membrane according to claim 2, wherein said membrane includes atleast one polyurethane including soft segments selected from the groupconsisting of polyether polyols, polyester polyols formed from thereaction product of a carboxylic acid and a diol wherein the repeatingunits of the reaction product have more than eight carbon atoms, ormixtures thereof.
 30. The membrane according to claim 29, wherein saidat least one polyurethane including soft segments selected from thegroup consisting of polyether polyols, polyester polyols formed from thereaction product of a carboxylic acid and a diol wherein the repeatingunits of the reaction product have more than eight carbon atoms, ormixtures thereof, is present in an amount of up to 30.0 wt. %.
 31. Themembrane according to claim 29, wherein the polyurethane including thepolyester polyol formed from a carboxylic acid and a diol wherein thereaction product has more than eight carbon atoms is selected from thegroup consisting of ethylene glycol isophthalate, 1,4 butanediolisophalate and 1,6 hexanediol isophthalate.
 32. The membrane accordingto claim 1, wherein said membrane has a gas transmission rate of lessthan about 10.0 for nitrogen gas wherein said membrane has an averagethickness of approximately 20.0 mils.
 33. The membrane according toclaim 32, wherein said membrane has a gas transmission rate of less thanabout 7.5 for nitrogen gas wherein said membrane has an averagethickness of approximately 20.0 mils.
 34. The membrane according toclaim 33, wherein said membrane has a gas transmission rate of less thanabout 5.0 for nitrogen gas wherein said membrane has an averagethickness of approximately 20.0 mils.
 35. The membrane according toclaim 34, wherein said membrane has a gas transmission rate of less thanabout 2.5 for nitrogen gas wherein said membrane has an averagethickness of approximately 20.0 mils.
 36. The membrane according toclaim 35, wherein said membrane has a gas transmission rate of less thanabout 2.0 for nitrogen gas wherein said membrane has an averagethickness of approximately 20.0 mils.
 37. The membrane according toclaim 1, wherein said membrane is elastomeric.
 38. The membraneaccording to claim 37, wherein said membrane has an elongation of atleast about 250%.
 39. The membrane according to claim 38, wherein saidmembrane has a elongation of between 250% to about 700%.
 40. Themembrane according to claim 37, wherein said membrane has a tensilestrength of at least about 2,500 psi.
 41. The membrane according toclaim 37, wherein said membrane has an 100% tensile modulus of between350 to about 3,000 psi.
 42. The membrane according to claim 1, whereinsaid membrane has a durometer hardness ranging from about 60 Shore A toabout 65 Shore D.
 43. The membrane according to claim 42, wherein saidmembrane has a durometer hardness ranging from about 80 Shore A to about55 Shore D.
 44. The membrane according to claim 43, wherein saidmembrane has a durometer hardness ranging from about 85 Shore A to about50 Shore D.
 45. The membrane according to claim 1, wherein saidpolyurethane is prepared from an isocyanate that is aromatic in nature.46. The membrane according to claim 45, wherein said isocyanate isdiphenylmethane diisocyanate.
 47. The membrane according to claim 1,wherein said polyurethane includes: (a) at least 50 wt. % of at leastone barrier material selected from the group consisting of co-polymersof ethylene and vinyl alcohol, polyvinylidene chloride, co-polymers ofacrylonitrile and methyl acrylate, polyethylene terephthalate, aliphaticand aromatic polyamides, crystalline polymers and polyurethaneengineering thermoplastics, said at least one barrier material beingblended with said polyurethane prior to forming said membrane; (b) 1 wt.% to about 50 wt. % of at least one aliphatic thermoplastic urethane;and (c) up to about 3 wt. % of one or more aromatic thermoplasticurethanes, wherein the total constituency of the blended layer is equalto 100 wt. %.
 48. The membrane according to claim 47, wherein saidaromatic thermoplastic urethane is selected from the group consisting ofpolyester, polyether, polycaprolactone, polyoxypropylene andpolycarbonate macroglycol based materials and mixtures thereof.
 49. Themembrane according to claim 47, wherein said thermoplastic is based onaromatic 1,4,diphenylmethane diisocyanate.
 50. The membrane according toclaim 1, wherein said membrane forms a first layer of a multi-layerstructure.
 51. The membrane according to claim 50, further comprising asecond layer formed from a material selected from the group consistingof co-polymers of ethylene and vinyl alcohol, polyvinylidene chloride,co-polymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, aliphatic and aromatic polyamides, crystalline polymers,polyurethane engineering thermoplastics and mixtures thereof which isbonded to said first layer.
 52. The membrane according to claim 51,wherein said first and second layers are formed together such thathydrogen bonding occurs between said first and second layers.
 53. Themembrane according to claim 51, wherein said first layer forms the outerlayer of a tire.
 54. The membrane according to claim 1, wherein saidmembrane is employed as a component of a wheel.
 55. The membraneaccording to claim 54, wherein said wheel is an inline or roller skatewheel.
 56. The membrane according to claim 1, wherein said membrane isformed at least in part from a thermoset material.
 57. The membraneaccording to claim 1, wherein said membrane is employed as part of anorthopedic device.
 58. The membrane according to claim 1, wherein saidmembrane is employed as a cushioning device incorporated as part of aprosthetic device.
 59. The membrane according to claim 1, wherein saidmembrane is employed as part of a flotation device.
 60. The membraneaccording to claim 59, wherein said flotation device is substantiallyrigid.
 61. The membrane according to claim 60, wherein said flotationdevice is part of a boat hull.
 62. The membrane according to claim 59,wherein said flotation device is flexible.
 63. The membrane according toclaim 62, wherein said flotation device is in the form of a tube orraft.
 64. The membrane according to claim 1, wherein said membrane isemployed as an inflatable component in athletic equipment.
 65. Themembrane according to claim 1, wherein said membrane is employed as acomponent of medical equipment.
 66. The membrane according to claim 65,wherein said medical equipment is in the form of a catheter balloon. 67.The membrane according to claim 1, wherein said membrane is employed asa fuel line.
 68. The membrane according to claim 1, wherein saidmembrane is employed as a fuel storage tank.
 69. A membrane comprising:a polyurethane including a polyester polyol, said membrane having adurability of at least 200,000 cycles under a KIM test analysis, whereinsaid membrane is in the form of a closed container having an averagewall thickness of 18 mils and is inflated with nitrogen gas to 20.0psig.
 70. The membrane according to claim 69, wherein said membrane hasa durability of more than 750,000 cycles under a KIM test analysis,wherein said membrane is in the form of a closed container having anaverage wall thickness of 18 mils and is inflated with nitrogen gas to20.0 psig.
 71. A membrane comprising: a polyurethane including apolyester polyol, said membrane having a yellowness index of 4.0 orless, wherein said membrane has an average wall thickness of 32 mils.72. The membrane according to claim 71, wherein said membrane has ayellowness index of 1.6 or less when said membrane has an averagethickness of 32 mils.
 73. A membrane comprising: a polyurethaneincluding a polyester polyol, said membrane having a total transmissionof light at a level of at least 90.0%, wherein said membrane has anaverage wall thickness of 32 mils.
 74. A substantially closed containercomprising: a polyurethane including a polyester polyol having a gastransmission rate of 15.0 or less for nitrogen gas wherein saidcontainer has an average thickness of approximately 20.0 mils.
 75. Thecontainer according to claim 74, wherein said polyester polyol of saidpolyurethane is selected from the group consisting of the reactionproduct of (a) a carboxylic acid having six or less carbon atoms and (b)a diol having six or less carbon atoms, wherein the repeating units ofthe polyester polyol formed by the aforesaid reaction has eight carbonatoms or less.
 76. The container according to claim 75, wherein thecarboxylic acid is selected from the group consisting of adipic,glutaric, succinic, malonic and oxalic acids, and mixtures thereof. 77.The container according to claim 75, wherein the diol is selected fromthe group consisting of ethylene glycol, propanediol, butanediol,neopentyldiol, pentanediol, hexanediol and mixtures thereof.
 78. Thecontainer according to claim 75, further comprising at least oneextender.
 79. The container according to claim 75, further comprising ahydrolytic stabilizer.
 80. The container according to claim 75, furthercomprising at least one plasticizer.
 81. The container according toclaim 75, further comprising at least one flame retardant.
 82. Thecontainer according to claim 75, wherein at least one additive isemployed, said additive being selected from the group consisting ofantioxidants, ultra-violet stabilizers, thermal stabilizers, lightstabilizers, organic anti-slip compounds, anti-block compounds,colorants, fungicides, mold release agents and lubricants, said at leastone additive being present in an amount of up to 3.0 wt. %.
 83. Thecontainer according to claim 75, wherein said polyurethane furthercomprises at least one soft segment selected from the group consistingof polyether polyols, polyester polyols formed from the reaction productof a carboxylic acid and a diol wherein the repeating unit of thereaction product has more than eight carbon atoms, or mixtures thereof.84. The container according to claim 83, wherein said polyurethaneincludes up to 30 wt. % of soft segments selected from the groupconsisting of polyether polyols, polyester polyols formed from thereaction product of at least one carboxylic acid and at least one diolwherein the repeating units of the reaction product thereof includesmore than eight carbon atoms, or mixtures thereof.
 85. The containeraccording to claim 74, further comprising at least one material selectedfrom the group consisting of co-polymers of ethylene and vinyl alcohol,polyvinylidene chloride, copolymers of acrylonitrile and methylacrylate, polyethylene terephthalate, aliphatic and aromatic polyamides,crystalline polymers and polyurethane engineering thermoplastics, saidmaterial being blended with said polyurethane prior to forming saidcontainer.
 86. The container according to claim 85, wherein saidcontainer includes up to about 70.0 wt. % polyester polyol basedurethane.
 87. The container according to claim 74, wherein saidcontainer has a gas transmission rate of less than about 10.0 fornitrogen gas wherein said container has an average thickness ofapproximately 20.0 mils.
 88. The container according to claim 87,wherein said container has a gas transmission rate of less than about7.5 for nitrogen gas wherein said container has an average thickness ofapproximately 20.0 mils.
 89. The container according to claim 74,wherein said container is elastomeric.
 90. The container according toclaim 89, wherein said container has an elongation of at least about250%.
 91. The container according to claim 89, wherein said containerhas a tensile strength of at least about 2,500 psi.
 92. The containeraccording to claim 89, wherein said container has an 100% tensilemodulus of between 350 to about 3,000 psi.
 93. The container accordingto claim 74, wherein said container has a durometer hardness rangingfrom about 60 Shore A to about 65 Shore D.
 94. The container accordingto claim 74, wherein said polyurethane is prepared from an isocyanatethat is aromatic in nature.
 95. The container according to claim 74,wherein said polyurethane includes: (a) at least 50 wt. % of at leastone barrier material selected from the group consisting of co-polymersof ethylene and vinyl alcohol, polyvinylidene chloride, co-polymers ofacrylonitrile and methyl acrylate, polyethylene terephthalate, aliphaticand aromatic polyamides, crystalline polymers and polyurethaneengineering thermoplastics, said at least one barrier material beingblended with said polyurethane prior to forming said container; (b) 1wt. % to about 50 wt. % of at least one aliphatic thermoplasticurethane; and (c) up to about 3 wt. % of one or more aromaticthermoplastic urethanes, wherein the total constituency of the blendedlayer is equal to 100 wt. %.
 96. The container according to claim 74,wherein said container is in the form of a multi-layer structureincluding at least first and second layers, said first layer comprisingsaid polyurethane including a polyester polyol which is formed from thereaction product of a carboxylic acid having six or less carbon atomsand a diol having six or less carbon atoms wherein the repeating unitsof the reaction product has eight carbon atoms or less.
 97. Thecontainer according to claim 96, further comprising a second layerformed from a material selected from the group consisting of co-polymersof ethylene and vinyl alcohol, polyvinylidene chloride, co-polymers ofacrylonitrile and methyl acrylate, polyethylene terephthalate, aliphaticand aromatic polyamides, crystalline polymers, polyurethane engineeringthermoplastics and mixtures thereof which is bonded to said first layer.98. The container according to claim 74, wherein said container ispermanently sealed.
 99. The container according to claim 98, whereinsaid container includes a captive gas.
 100. The container according toclaim 74, wherein said container is in the form of a supporting element.101. The container of according to claim 100, wherein said supportelement is incorporated into an article of furniture.
 102. The containeraccording to claim 101, wherein said article of furniture is a chair.103. The container according to claim 102, wherein said supportingelement is a lumbar support structure.
 104. The container according toclaim 74, wherein said container is in the form of an inflatable ball.105. A cushioning device formed from a membrane comprising: apolyurethane including a polyester polyol, said membrane having a gastransmission rate of less than about 15.0 for nitrogen gas wherein saidmembrane has an average thickness of approximately 20.0 mils.
 106. Thecushioning device according to claim 105, wherein said polyester polyolof said polyurethane is selected from the group consisting of thereaction product of (a) a carboxylic acid having six or less carbonatoms and (b) a diol having six or less carbon atoms, wherein therepeating units of the polyester polyol formed by the aforesaid reactionhas eight carbon atoms or less.
 107. The cushioning device according toclaim 106, wherein the carboxylic acid is selected from the groupconsisting of adipic, glutaric, succinic, malonic and oxalic acids, andmixtures thereof.
 108. The cushioning device according to claim 106,wherein the diol is selected from the group consisting of ethyleneglycol, propanediol, butanediol, neopentyldiol, pentanediol, hexanedioland mixtures thereof.
 109. The cushioning device according to claim 106,further comprising at least one extender.
 110. The cushioning deviceaccording to claim 106, further comprising a hydrolytic stabilizer. 111.The cushioning device according to claim 106, further comprising atleast one plasticizer.
 112. The cushioning device according to claim106, further comprising at least one flame retardant.
 113. Thecushioning device according to claim 106, wherein at least one additiveis employed, said additive being selected from the group consisting ofantioxidants, ultra-violet stabilizers, thermal stabilizers, lightstabilizers, organic anti-block compounds, colorants, fungicides, moldrelease agents and lubricants, said at least one additive being presentin an amount of up to 3.0 wt. %.
 114. The cushioning device according toclaim 106, wherein said polyurethane includes at least one filler, saidfiller being present in an amount of up to 60 wt. %.
 115. The cushioningdevice according to claim 106, wherein said cushioning device includesat least one polyurethane including soft segments selected from thegroup consisting of polyether polyols, polyester polyols formed from thereaction product of a carboxylic acid and a diol wherein the repeatingunits of the reaction product has more than eight carbon atoms, andmixtures thereof.
 116. The cushioning device according to claim 106,wherein said polyurethane includes up to 30 wt. % of soft segmentsselected from the group consisting of polyether polyols, polyesterpolyols formed from the reaction product of at least one carboxylic acidand at least one diol wherein the repeating units of the reactionproduct thereof includes more than eight carbon atoms, or mixturesthereof.
 117. The cushioning device according to claim 105, furthercomprising at least one material selected from the group consisting ofco-polymers of ethylene and vinyl alcohol, polyvinylidene chloride,co-polymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, aliphatic and aromatic polyamides, crystalline polymersand polyurethane engineering thermoplastics, said material being blendedwith said polyurethane prior to forming said cushioning device.
 118. Thecushioning device according to claim 105, wherein said cushioning devicehas a gas transmission rate of less than about 10.0 for nitrogen gaswherein said cushioning device has an average thickness of approximately20.0 mils.
 119. The cushioning device according to claim 118, whereinsaid cushioning device has a gas transmission rate of less than about7.5 for nitrogen gas wherein said cushioning device has an averagethickness of approximately 20.0 mils.
 120. The cushioning deviceaccording to claim 105, wherein said cushioning device is elastomeric.121. The cushioning device according to claim 120, wherein saidcushioning device has an elongation of at least about 250%.
 122. Thecushioning device according to claim 120, wherein said cushioning devicehas a tensile strength of at least about 2,500 psi.
 123. The cushioningdevice according to claim 120, wherein said cushioning device has an100% tensile modulus of between 350 to about 3,000 psi.
 124. Thecushioning device according to claim 105, wherein said cushioning devicehas a durometer hardness ranging from about 60 Shore A to about 65 ShoreD.
 125. The cushioning device according to claim 105, wherein saidpolyurethane is prepared from an isocyanate that is aromatic in nature.126. The cushioning device according to claim 105, wherein saidpolyurethane includes: (a) at least 50 wt. % of at least one barriermaterial selected from the group consisting of co-polymers of ethyleneand vinyl alcohol, polyvinylidene chloride, co-polymers of acrylonitrileand methyl acrylate, polyethylene terephthalate, aliphatic and aromaticpolyamides, crystalline polymers and polyurethane engineeringthermoplastics, said at least one barrier material being blended withsaid polyurethane prior to forming said membrane; (b) 1 wt. % to about50 wt. % of at least one aliphatic thermoplastic urethane; and (c) up toabout 3 wt. % of one or more aromatic thermoplastic urethanes, whereinthe total constituency of the blended layer is equal to 100 wt. %. 127.The cushioning device according to claim 105, wherein said cushioningdevice is in the form of a multi-layer structure including at leastfirst and second layers, said first layer comprising said polyurethaneincluding a polyester polyol which is formed from the reaction productof a carboxylic acid having six or less carbon atoms and a diol havingsix or less carbon atoms wherein the repeating units of the reactionproduct has eight carbon atoms or less.
 128. The cushioning deviceaccording to claim 127, further comprising a second layer formed from amaterial selected from the group consisting of co-polymers of ethyleneand vinyl alcohol, polyvinylidene chloride, co-polymers of acrylonitrileand methyl acrylate, polyethylene terephthalate, aliphatic and aromaticpolyamides, crystalline polymers, polyurethane engineeringthermoplastics and mixtures thereof which is bonded to said first layer.129. The cushioning device according to claim 105, wherein saidcushioning device is employed as part of a seat.
 130. The cushioningdevice according to claim 129, wherein said seat is a bicycle seat. 131.The cushioning device according to claim 129, wherein said seat is asaddle.
 132. The cushioning device according to claim 105, wherein saidcushioning device is incorporated into protective equipment.
 133. Thecushioning device according to claim 132, wherein said protectiveequipment is a shin guard.
 134. The cushioning device according to claim132, wherein said protective equipment is a helmet.
 135. The cushioningdevice according to claim 105, wherein said cushioning device is acomponent of a shoe.
 136. The cushioning device according to claim 135,wherein said shoe includes an upper and a sole, said cushioning devicebeing in the form of an inflatable bladder incorporated as a portion ofsaid sole.
 137. The cushioning device according to claim 136, whereinsaid inflatable bladder serves as a portion of an outsole which is atleast partially exposed to the atmosphere.
 138. The cushioning deviceaccording to claim 136, wherein said inflatable bladder is formed atleast in part of a thermoset material.
 139. The cushioning deviceaccording to claim 136, wherein said inflatable bladder includes atleast one port for the selective introduction of a fluid.
 140. Thecushioning device according to claim 139, wherein said fluid is a gas.141. The cushioning device according to claim 140, wherein said gas isat a pressure of greater than 0 psig.
 142. The cushioning deviceaccording to claim 136, wherein said inflatable bladder has an averagethickness of between 5 to about 60 mils.
 143. The cushioning deviceaccording to claim 142, wherein said inflatable bladder has an averagethickness of between 15 to about 40 mils.
 144. The cushioning deviceaccording to claim 105, wherein said membrane is a component of a skate.145. The cushioning device according to claim 105, wherein saidcushioning device has a durability of at least 200,000 cycles under aKIM test analysis, wherein said cushioning device has an averagethickness of 18 mils and is inflated with nitrogen gas to 20.0 psig.146. The cushioning device according to claim 145, wherein saidcushioning device has a durability of more than 750,000 cycles under aKIM test analysis, wherein said cushioning device has an average wallthickness of 18 mils and is inflated with nitrogen gas to 20.0 psig.147. The cushioning device according to claim 105, wherein saidcushioning device has a yellowness index of 4.0 or less, wherein saidmembrane has an average wall thickness of 32 mils.
 148. The cushioningdevice according to claim 147, wherein said cushioning device has ayellowness index of 1.6 or less, wherein said cushioning device has anaverage thickness of 32 mils.
 149. The cushioning device according toclaim 105, wherein said cushioning device has a total transmission oflight at a level of at least 90.0 %, wherein said cushioning device hasan average wall thickness of 32 mils.
 150. A hydropneumatic accumulatorformed from a membrane comprising: a polyurethane including a polyesterpolyol, said membrane having a gas transmission rate of 15.0 or less fornitrogen gas wherein said membrane has an average thickness ofapproximately 20.0 mils.
 151. The accumulator according to claim 150,wherein said polyester polyol of said polyurethane is selected from thegroup consisting of the reaction product of (a) a carboxylic acid havingsix or less carbon atoms and (b) a diol having six or less carbon atoms,wherein the repeating units of the polyester polyol formed by theaforesaid reaction has eight carbon atoms or less.
 152. The accumulatoraccording to claim 151, wherein the carboxylic acid is selected from thegroup consisting of adipic, glutaric, succinic, malonic and oxalicacids, and mixtures thereof.
 153. The accumulator according to claim151, wherein the diol is selected from the group consisting of ethyleneglycol, propanediol, butanediol, neopentyldiol, pentanediol, hexanedioland mixtures thereof.
 154. The accumulator according to claim 151,further comprising at least one extender.
 155. The accumulator accordingto claim 151, further comprising a hydrolytic stabilizer.
 156. Theaccumulator according to claim 151, wherein said polyurethane includesat least one plasticizer, said plasticizer being present in an amount ofup to 40.0 wt. %
 157. The accumulator according to claim 151, whereinsaid polyurethane includes at least one flame retardant, said flameretardant being present in an amount of up to 40.0 wt. %.
 158. Theaccumulator according to claim 151, wherein at least one additive isemployed, said additive being selected from the group consisting ofantioxidants, ultra-violet stabilizers, thermal stabilizers, lightstabilizers, organic anti-slip compounds, anti-block compounds,colorants, fungicides, mold release agents and lubricants, said at leastone additive being present in an amount of up to 3.0 wt. %.
 159. Theaccumulator according to claim 151, wherein said accumulator includes atleast one polyurethane including soft segments selected from the groupconsisting of polyether polyols, polyester polyols formed from thereaction product of a carboxylic acid and a diol wherein the repeatingunits of the reaction product has more than eight carbon atoms, andmixtures thereof.
 160. The accumulator according to claim 151, whereinsaid polyurethane includes up to 30 wt. % of soft segments selected fromthe group consisting of polyether polyols, polyester polyols formed fromthe reaction product of at least one carboxylic acid and at least onediol wherein the repeating units of the reaction product thereofincludes more than eight carbon atoms, or mixtures thereof.
 161. Theaccumulator according to claim 150, wherein said accumulator furthercomprises at least one material selected from the group consisting ofco-polymers of ethylene and vinyl alcohol, polyvinylidene chloride,co-polymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, aliphatic and aromatic polyamides, crystalline polymersand polyurethane engineering thermoplastics, said material being blendedwith said polyurethane prior to forming said accumulator.
 162. Theaccumulator according to claim 161, wherein said accumulator includes upto about 70.0 wt. % polyester polyol based urethane.
 163. Theaccumulator according to claim 150, wherein said accumulator has a gastransmission rate of less than about 10.0 for nitrogen gas wherein saidaccumulator has an average thickness of approximately 20.0 mils. 164.The accumulator according to claim 163, wherein said accumulator has agas transmission rate of less than about 7.5 for nitrogen gas whereinsaid accumulator has an average thickness of approximately 20.0 mils.165. The accumulator according to claim 150, wherein said accumulator iselastomeric.
 166. The accumulator according to claim 165, wherein saidaccumulator has an elongation of at least about 250%.
 167. Theaccumulator according to claim 165, wherein said accumulator has atensile strength of at least about 2,500 psi.
 168. The accumulatoraccording to claim 165, wherein said accumulator has an 100% tensilemodulus of between 350 to about 3,000 psi.
 169. The accumulatoraccording to claim 150, wherein said accumulator has a durometerhardness ranging from about 60 Shore A to about 65 Shore D.
 170. Theaccumulator according to claim 150, wherein said polyurethane isprepared from an isocyanate that is aromatic in nature.
 171. Theaccumulator according to claim 150, wherein said polyurethane includes:(a) at least 50 wt. % of at least one barrier material selected from thegroup consisting of co-polymers of ethylene and vinyl alcohol,polyvinylidene chloride, co-polymers of acrylonitrile and methylacrylate, polyethylene terephthalate, aliphatic and aromatic polyamides,crystalline polymers and polyurethane engineering thermoplastics, saidbarrier material being blended with said polyurethane prior to formingsaid accumulator; (b) 1 wt. % to about 50 wt. % of at least onealiphatic thermoplastic urethane; and (c) up to about 3 wt. % of one ormore aromatic thermoplastic urethanes, wherein the total constituency ofthe blended layer is equal to 100 wt. %.
 172. The accumulator accordingto claim 150, wherein said accumulator is in the form of a multi-layerstructure including at least first and second layers, said first layercomprising said polyurethane including a polyester polyol which isformed from the reaction product of a carboxylic acid having six or lesscarbon atoms and a diol having six or less carbon atoms wherein therepeating units of the reaction product has eight carbon atoms or less.173. The accumulator according to claim 172, further comprising a secondlayer formed from a material selected from the group consisting ofco-polymers of ethylene and vinyl alcohol, polyvinylidene chloride,co-polymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, aliphatic and aromatic polyamides, crystalline polymers,polyurethane engineering thermoplastics and mixtures thereof which isbonded to said first layer.
 174. The accumulator according to claim 150,wherein said accumulator separates two fluids.
 175. The accumulatoraccording to claim 174, wherein said fluids include a gas disposed alongone side of said accumulator and a liquid disposed along another side ofsaid accumulator.
 176. A method for producing a laminated membraneuseful for controlling gas permeation therethrough, comprising the stepsof: (a) extruding a first layer of polyurethane including a polyesterpolyol; and (b) extruding a second layer of material together with saidfirst layer, said second layer including functional groups with hydrogenatoms which are capable of participating in hydrogen bonding with saidfirst layer of polyurethane to form a membrane; said membrane beingcharacterized in that the resulting membrane has a gas transmission rateof 15.0 or less for nitrogen gas when said membrane has an averagethickness of 20.0 mils.
 177. The method according to claim 176, whereinsaid membrane has a tensile strength of at least about 2,500 psi. 178.The method according to claim 176, wherein said membrane has an 100%tensile modulus of between 350 to about 3,000 psi.
 179. The methodaccording to claim 176, wherein said membrane has a durometer hardnessranging from about 60 Shore A to about 65 Shore D.
 180. The methodaccording to claim 176, wherein said first and second layers arelaminated together at a pressure of at least 200 psi.
 181. The methodaccording to claim 176, wherein said first and second layers areextruded simultaneously.
 182. The method according to claim 176, whereinthe average thickness of said first and second layers can be varied overthe length of the membrane.
 183. The method according to claim 176,wherein said membrane has a durability of at least 200,000 cycles undera KIM test analysis wherein said membrane is in the form of a closedcontainer having an average wall thickness of 18 mils and is inflatedwith nitrogen gas to 20.0 psig.